Source: Martha Stewart Weddings, Spring 2006
- 6 large eggs, separated
- 1 1/2 cups sugar
- 2 cups whole milk
- 1 teaspoon pure vanilla extract
- 6 cups (12 sticks) unsalted butter, softened
For Caramel Buttercream Variation:
Put egg yolks and 1/2 cup sugar into the bowl of an electric mixer fitted with the whisk attachment; beat on high speed until pale and thickened, 2 to 3 minutes.
Bring milk and vanilla to a boil in a medium saucepan. Remove from heat. Whisk about one-third of the liquid into yolk mixture. Pour mixture back into pan with remaining custard; whisk to combine. Cook over medium heat, stirring constantly, until mixture registers 185 degrees on an instant-read thermometer. Remove from heat; strain. Refrigerate until cool.
Put butter into the bowl of an electric mixer fitted with the paddle attachment; mix on medium-high speed until pale and fluffy. Mix in chilled custard.
Heat egg whites and remaining 1 cup sugar in the clean heatproof bowl of an electric mixer set over a pan of simmering water, whisking constantly, until sugar has dissolved. Attach bowl to mixer fitted with the whisk attachment; beat on high speed until stiff peaks form.
Add egg-white mixture to butter mixture; beat on medium-high speed until smooth. Refrigerate in an airtight container up to 3 days; bring to room temperature, and beat before using.
For Caramel Buttercream Variation
Add caramel cream cheese filling.