German Buttercream Frosting

Method - Make milk mixture: In a medium saucepan (preferably one with sloped sides), whisk together the sugar, cornstarch, and salt until combined. Add about 1/4 cup of milk to the sugar mixture, whisking to form a thick paste. This will keep the mixture from forming clumps when you add the remaining milk. Add the rest of the milk to the pot, whisking to incorporate it.

Method - Bring milk mixture to a simmer: Turn the stove on to medium heat and bring the milk mixture to a gentle simmer, which will take 5 to 6 minutes. Tiny bubbles will rise to the surface and calmly break. The surface of the liquid should barely move. Remove the pot from the heat.

Method - Beat the eggs: Use a fork to lightly beat the egg yolks until they are runny.

Method - Temper the egg yolks: Slowly pour a cup of the warm milk mixture in a thin, steady stream into the bowl with the eggs while whisking constantly. Once combined slowly pour the milk-egg mixture in a slow, steady stream into the saucepan of hot milk while whisking constantly. You now have the base for custard.

Method - Finish the custard: Return the pot to the stove and heat the custard mixture to a gentle simmer over medium-low heat, constantly stirring with the whisk. The mixture will thicken considerably in 2 to 3 minutes. In order to tell if the custard is ready: dip a spoon in the custard and it should be thick enough for its edges to hold a line drawn with your finger on the back of the spoon. Stir in the vanilla extract until the mixture is smooth and combined.

Method - Cover and chill the custard: Cover and chill the custard until cool (or until it reaches room temperature). You can press a piece of plastic wrap directly onto the surface of the custard and chill it for up to 2 days in the refrigerator. If you chill it, it needs to be brought to room temperature before proceeding.

Method - Whip the butter in a stand mixer: In the bowl of your stand mixer fitted with the whisk attachment add the butter. Turn the mixer to medium and gradually bring the mixer speed up to high speed to whip the butter until very light, fluffy, and almost white in appearance, 5 to 6 minutes. Stop the mixer and scrape down the bowl once or twice during this whipping process.

Method - Add custard to the butter: While the butter is whipping, give the chilled custard a thorough stir to make it smooth. Decrease the mixer's speed to medium-low and add the custard to the butter in the bowl 1 tablespoonful at a time. Allow the custard to be fully incorporated before adding the next tablespoonful. Scrape down the bowl often while adding the custard to make sure it's properly incorporated.

Method - Whip buttercream on medium-high: Once the custard has been added, increase the mixer's speed to medium-high and whip until the mixture is light and fluffy, 2 to 3 minutes.

Method - Store buttercream: Once mixed, use the buttercream as desired. Store in a food storage container for up to 4 days or freeze for up to 2 months.

Method - Re-whip buttercream: To re-whip from the fridge: The buttercream will need to warm up at room temperature for 10 minutes before mixing on low speed until it's smooth again. To re-whip from frozen: Soften the buttercream again by gently heating the frosting over a double boiler (a bowl set over a pot of gently simmering water). If you have a butane torch, you can also zap the bottom of your mixer bowl with the flame to warm it slightly. When the buttercream starts to become glossy, whip it on medium-high speed (#5 on a KitchenAid) until smooth. If you went a little trigger happy with heating the buttercream, just pop it back into the fridge to cool it down before whipping until fluffy.