Yields: about 550g (2½ C) of buttercream. Enough to frost 1 cake or about 10 cupcakes.
Ingredients
150ml milk
50g (or ¼ cup) granulated sugar
1 teaspoon vanilla extract
1 teaspoon cornstarch
3 egg yolks
50g (or ¼ cup) granulated sugar
200g (or ¾ cup + 2 tablespoons) unsalted butter, at room temperature
Instructions
First, make a simple custard. In a small combine, combine the milk, 50g of sugar and the vanilla. Gently heat over low heat, stirring occasionally. In a heatproof bowl, combine the cornstarch with a little splash of the milk mixture. Stir to a smooth paste. Add another splash of milk an stir to incorporate. Whisk in the egg yolks and sugar until frothy and well combined. Once the milk mixture has reached boiling point and bubbles start to appear around the edges of the pan, slowly drizzle the hot milk into the egg mixture, whisking continuously. Once all the milk has been added, pour the mixture back into the saucepan and heat over low heat. Whisking continuously, wait until the first bubbles appear and the mixture has thickened. Pour into a clean heatproof bowl and place a piece of plastic wrap directly onto the surface of the custard to prevent a skin from forming. Allow to cool to body temperature.
Once the custard has cooled sufficiently, mix in the butter, 1 tablespoon at a time, waiting until each tablespoon of butter is incorporated before adding the next. Use immediately or cover with plastic wrap and place in the fridge until needed. Store in the fridge for up to 1 week or for up to 2 months in the freezer in a freeze-proof container or bag.
To use buttercream that has been refrigerated, allow to come to room temperature (this takes about 3 hours in a warm kitchen) or microwave in 30 second intervals, stirring in between each interval, until it's soft. Then mix through until it's spreadable again. Thaw frozen buttercream in the fridge overnight, then allow to come to room temperature before use and, once at room temperature, mix briefly until smooth.
Serve at room temperature. If you've assembled a cake or decorated cupcakes, allow cake or cupcakes to come to room temperature before serving (about 3 hours in a warm kitchen).
Recipe by The Tough Cookie at https://thetoughcookie.com/2013/12/02/battle-of-the-buttercreams-iv-german-buttercream/