Makes about 280g, or about 1½ cups. Enough to generously frost 6-8 cupcakes. Making caramel German buttercream won't take long, but bear in mind that the custard needs time to cool.
Ingredients
For the caramel:
120g (or ½ cup + 5 teaspoons) granulated sugar
2 tablespoons water
60ml (or ¼ cup) heavy whipping cream
To turn it into buttercream:
2 large egg yolks (about 2 tablespoons)
1 teaspoon cornstarch
100ml (or ⅓ cup + 4 teaspoons) regular milk
pinch of table salt
175g (or ¾ cup + 1 teaspoon) unsalted butter, softened at room temperature
Instructions
Start by making caramel:
Fill your kitchen sink with about 5-cm/2-inches of cold water. Once the caramel is done, you need to dunk the bottom of the pan in this cold water bath to stop the cooking process.
Add the sugar and the water to a medium-sized, light-colored saucepan. The light color of the saucepan makes it easy to monitor the color of the caramel as it cooks. Heat over low heat, stirring with a metal spoon until the sugar has dissolved.
Crank up the heat to medium-high and cook to a golden caramel. Don't stir it at this point. The syrup will first start to caramelize at the edge of the pan. Once this happens, you can gently whisk the caramel to get an even color.
Once you're happy with the color of the caramel, turn the heat down and carefully drizzle in the cream, whisking continuously. The caramel will bubble and sizzle, so be careful. Once all the cream has been added, turn the heat down, stop whisking and allow to cook for 1 minute. Then remove the pan from the heat and dunk the bottom of the pan into the water bath in the sink.
There is no need to cool the caramel. You just need to stop the cooking process so the caramel won't become too dark.
Proceed by making a caramel custard:
In a medium-sized bowl, whisk together the yolks, cornstarch and two tablespoons of the milk until the yolk mixture looks foamy and smooth. Add the rest of the milk and the salt to the caramel in the saucepan.
Place the saucepan over low heat, whisking to dissolve the caramel into the milk Once the caramel has dissolved, crank the heat up to medium-high and scald the milk mixture. Once the first bubbles appear, remove the pan from the heat and carefully pour the hot milk mixture into the yolk mixture, whisking continuously to keep the eggs from scrambling.
Once combined, pour the mixture back into the saucepan. Heat over low heat, whisking continuously, until the first bubbles appear and the mixture thickens considerably.
Remove the pan from the heat and whisk for another minute to knock some of the heat out. Pour the caramel custard onto a clean plate and immediately cover it with plastic wrap, pressing the plastic wrap directly onto the custard. This keeps a skin from forming. Allow the custard to cool completely.
Once the custard has cooled, beat the butter in a medium-sized bowl until smooth and fluffy and lightened in color, about 2 minutes. Add the cooled custard, one tablespoon at a time, mixing well after each addition. Once all the custard has been added, mix for another few minutes, until the buttercream looks thick, smooth and creamy. This buttercream is a bit softer than vanilla German buttercream, but it should pipe just as beautifully.
Use immediately or store in an airtight container or a zipper bag in the fridge for up to two weeks or in the freezer for up to two months. To use buttercream that has either been refrigerated or frozen, first allow to come to room temperature then beat until smooth and spreadable again.
Cakes or cupcakes decorated with buttercream generally keep up to 3 days, stored in an airtight container in the fridge. Allow buttercream to come to room temperature before serving (for a big cake, this may take up to four hours!).
Recipe by The Tough Cookie at https://thetoughcookie.com/2015/10/18/german-caramel-buttercream/