If you are making my strawberry cake recipe, I highly recommend saving aside the strawberry juice (left over after you made strawberry puree) and substitute the juice for the water in the syrup. If you want a lemon meringue buttercream, beat in some lemon curd (this is a great use for the leftover yolks). You can also beat in a variety of other flavors (almond extract, peppermint extract, etc.) If you are making another flavor (like using lemon curd or strawberry), use half the amount of vanilla called for.
Italian Meringue Buttercream
Enough to ice a double-layer 9 or 10-inch cake.1 C sugar
1/3 C water
4 large egg whites
1 tsp cream of tartar
5 sticks (2.5 cups) unsalted butter (at room temp) pinch salt
1 Tbsp vanilla
1. In a saucepan combine sugar and water and bring to a boil, stirring until sugar is dissolved.
2. Simmer syrup for 3-5 minutes.
3. While the syrup is on the stove, in a standing electric mixer beat egg whites using the the paddle attachment with a pinch of salt until foamy.
4. Beat in cream of tarter and continue beating the whites until they just hold stiff peaks.
5. While the mixer is running, slowly pour in the sugar syrup (hot off the stove) in a stream, avoiding the beater blade.
6. Beat mixture at medium speed until completely cool, around 15-20 minutes.
7. Beat in the butter, 1 tablespoon at a time, and continue to beat until it is thick and smooth. If it looks lumpy or curdled/oily, just keep beating. Crank up that mixer and beat until it is nice and smooth. It might take awhile - just keep beating! The key here is that the butter and the egg white/sugar mixture needs to be as similar a temperature as possible. If they didn't start that way, they will end up there if you just keep beating.
8. Once it reaches the proper consistency, beat in the vanilla.
