It’s rhubarb season, so time for an old favorite: rhubarb and custard. In cupcake form! These fluffy vanilla cupcakes are filled with a tangy rhubarb puree and topped with a swirl of custard buttercream, rhubarb syrup and crunchy crumbs!
About a week ago, one of my favorite Youtubers Cupcake Jemma baked up a batch of Rhubarb Crumble & Custard Cupcakes. And I was like: wait, what? Rhubarb? Already?! But yes, of course: “rhubarb already”. After all, it’s almost Mother’s Day!
I have a GREAT mom (hi Mom!), and she happens to love rhubarb. As I’ve made her rhubarb-y sweets for Mother’s Day a couple of times, the two are now inextricably connected in my mind.
Mother’s Day = rhubarb is in season!
And now that we’re on the subject of Mother’s Day, I’m celebrating my SECOND Mother’s Day as a mom this year (again: wait? what?), which makes me feel so proud and grown up! I think I’m going to wear a plastic tiara for the occasion. Or maybe brush a handful a glitter in my hair? I’m not sure yet, but it’s gonna be something festive. I can’t wait to find out what the Rocking Rebel has planned for me, but since Mother’s Day is ALSO the Rocking Rebel’s birthday this year, I’ve got a lot of things planned for him (a birthday party/picnic in the park, with a choice of different kinds of apple pie, to be specific)!
(Btw, if you’re an apple person, like the Rocking Rebel, you MUST check out his recipe for Apple Cookie Crumb Cake. It’s delicious!)
But wait, back to these rhubarb and custard cupcakes.
These cupcakes are inspired and partly adapted from Jemma’s recipe. Being the baking-know-it-all that I am (wait. Let’s change that to: super-experienced-and-seasoned-home-baker-who-intuitively-knows-how-to-make-recipes-work, shall we?) I changed her recipe a bit.
First of all, I used my own perfect vanilla cupcake recipe for the cake part. Jemma’s cupcakes are actually vanilla cupcakes with a rhubarb ripple, but I didn’t feel like taking the ripple route. Too much of a hassle.
I’ve also come up with my own recipe for custard buttercream because Jemma’s recipe was a little vague on that.
Btw, this custard buttercream is SOOOO good! If you like German buttercream (who doesn’t?!) this custard buttercream is right up your alley. It’s made by beating pastry cream (which is after all a fancy name for custard) into beaten butter. (And yes, that means I’m using the Beaten Butter Method for this buttercream!). It’s easy to make, but make sure the custard, which is very thick, doesn’t catch on the bottom of the pan as you cook it!
Next, I adapted Jemma’s recipe for the rhubarb puree – or goo, as she calls it – because I found the orange and vanilla in her recipe a little too strong.
The rhubarb goo is made by combining rhubarb (use the red or pinks stalks for a pink puree!), sugar, water, vanilla, and a little orange zest in a baking tray, covering it tightly with aluminum foil, and baking it for about 20 minutes. The rhubarb will break down, and you’ll be able to strain the liquid off. The liquid is turned into a tangy rhubarb syrup which is then drizzled on top of the cupcakes, while the rhubarb is blitzed in a food processor to make a fine puree.
Finally, the crunchy crumbs sprinkled on top give the cupcakes a bit of bite and more of a rhubarb-crumble feel. They’re also very yummy!
But oh, that custard buttercream! Confession: I had some leftover after I finished decorating the cupcakes, and I, um, just ate it. With a spoon. It’s THAT good! 😉
Anyway, that’s all about today’s recipe. But if you like this post, click here to subscribe to my mailing list and get my mini eCookbook for FREE (because you’re awesome), scroll down for a nice pin, and share this post with all your cupcake and rhubarb-loving friends!
Or, if you need more rhubarb in your life, check out these awesome rhubarb recipes:
- Vanilla Ice Cream with Rhubarb and a Cookie Swirl ← super summery!
- or Strawberry Mousse Cake with Candied Rhubarb ← prettiest cake ever?
- or Rhubarb and Vanilla Jam ← Really easy. Really good.
- 150g (or 5.3 oz) washed and trimmed pink/red rhubarb
- 1 tablespoon granulated sugar
- zest of ¼ orange
- ¼ teaspoon vanilla extract
- 1½ teaspoons water
- 60g (or ¼ cup + ¾ teaspoon) unsalted butter, softened at room temperature
- 60g (or ¼ cup + 2½ teaspoons) granulated sugar
- 1 large egg (about 50g)
- 60g (or ½ cup – 1 teaspoon) all-purpose flour
- ¾ teaspoon baking powder
- ⅛ teaspoon baking soda
- pinch of salt
- 2¼ teaspoons buttermilk
- ⅛ teaspoon vanilla extract
- 150g (or ½ cup + 2 tablespoons) milk, I used 2% milk
- 100g (or ½ cup) granulated sugar
- 20g (or 4 teaspoons) cornstarch
- 2 large egg yolks
- 226g (or 1 cup) unsalted butter
- ¼ teaspoon vanilla extract
- 39g (or ¼ cup + 1 tablespoon + ¼ teaspoon) all-purpose flour
- 10g (or 5 teaspoons) rolled oats
- 1 teaspoon granulated sugar
- pinch of table salt
- 25g (or 5¼ teaspoons) melted unsalted butter
- Preheat oven to 175°C/350°F (standard oven setting).
- Chop the rhubarb into 5-cm/2-inch chunks. Place in the bottom of a medium-sized roasting tray in a single layer and sprinkle with the sugar. Add the orange zest. Next, mix the vanilla with the water and drizzle it oven the rhubarb.
- Wrap the roasting tray tightly in aluminum foil and bake in the middle of the oven for 20-25 minutes (now’s the time to make the cupcake batter). Remove from oven and allow to cool a bit so you can handle the tray.
- Pour the contents of the roasting tray (broken down rhubarb and liquid) into a strainer set over a small saucepan to catch the liquid. Don’t press down on the rhubarb, or you’ll get rhubarb bits in the syrup. Just let the liquid drain off. Set the liquid aside.
- Next, place what’s left in the strainer (the rhubarb) in the bowl of a food processor and blitz to a fine puree. Allow to cool completely.
- Place the pan with the rhubarb liquid over low heat. Allow to come to a simmer. Reduce by half by letting it bubble gently for 2-3 minutes.
- Pour in a heatproof container (a mug) and allow to cool to room temperature.
- Preheat oven to 170°C/340°F (standard oven setting) and line a 6-cup muffin pan with cupcake liners.
- In a medium-sized bowl, beat butter until pale and fluffy, about two minutes. Add the sugar and mix until the mixture looks light and fluffy, another 2 minutes.
- Crack the egg in a small bowl and whisk with a fork. Add half the egg to the butter and sugar mixture and mix until well combined. Add the remaining half egg and mix until the mixture looks like thick buttercream. The mixture may separate, but if you just keep mixing it will come together again. Make sure to scrape the sides and bottom of the bowl every now and then with a rubber spatula.
- Add the flour, baking powder, baking soda and salt and stir with a rubber spatula until somewhat incorporated. Mix briefly with the mixer, about 30 seconds, then scrape the sides and bottom of the bowl again with your rubber spatula and mix for another 5 seconds. Finally, add the buttermilk and vanilla and mix for 30 seconds, or until beautifully combined.
- Divide the batter evenly over the lined cups, place in the middle of the oven and bake for 20 minutes, or until a tester inserted into the center of one of the cupcakes comes out clean. Allow to cool to room temperature on a wire rack before frosting.
- Combine milk and ¾ of the sugar in a small saucepan. Add the remaining sugar with the cornstarch to a medium-sized, heatproof bowl. Whisk until combined. Add about 4 tablespoons of the milk mixture to the cornstarch mixture and whisk until incorporated. Add the egg yolks and whisk until frothy.
- Place milk-and-sugar mixture over low heat and heat gently until scalding. Drizzle the hot milk mixture into the bowl with the yolk-mixture, whisking constantly.
- Once all the milk has been added, pour the yolky-mixture back into the saucepan and heat over low heat, stirring constantly with a rubber, heatproof spatula. As the mixture heats, it will thicken. Keep scraping the sides and bottom of the pan and heat the mixture through for another minute, making sure the custard doesn’t catch on the bottom of the pan.
- Once heated through, scrape the custard onto a plate and cover immediately with plastic wrap, pressing the plastic wrap directly onto the surface of the custard with your hand (be careful: hot!) to prevent a skin from forming. Set aside to cool to room temperature.
- Once the pastry cream has cooled to room temperature, add butter to the bowl of a stand mixer fitted with the paddle attachment. Beat butter until light and fluffy.
- Add the pastry cream one spoonful at a time, mixing well after each addition. Once all the pastry cream has been added, add the vanilla and beat for another 2-5 minutes, or until the buttercream looks smooth, creamy and fluffy.
- Preheat oven to 170°C/340°F (standard oven setting).
- Combine all ingredients in a small bowl. Using a wooden spoon, stir until incorporated. Using your fingers, form fine crumbs. Spread the crumbs on a small cookie sheet and bake on a rack in the middle of the oven for 10-15 minutes, or until golden brown.
- Remove from the oven and allow to cool completely to room temperature.
- Using an apple corer, remove the center of each cupcake. Fill a small piping bag with the rhubarb goo, snip the end of the piping bag, and fill the holes with the rhubarb goo.
- Fit a large piping bag with a star tip and fill it with the custard buttercream. Pipe large swirls on top of the cupcakes (you will probably have some leftover buttercream), drizzle with the rhubarb syrup, and sprinkle with crumbs.
- Cupcakes keep in an airtight container in the fridge for 3 days. Allow to come to room temperature before serving.