2 1/4 c (293 g) cake flour
1 Tbsp baking powder
1/2 tsp salt
1 1/4 c (296 ml) buttermilk (or whole milk + 1ish Tbsp vinegar, left to curdle)
4 egg whites
1 tsp vanilla
1 1/2 c (300 g) sugar
1/2 c (118 g) butter, room temp
1/2 c (118 ml) raspberries
Preheat your oven to 350F and line two cupcake tins with liners.
Sift together the flour, baking powder and salt, then set aside.
Mix together the buttermilk, egg whites and vanilla in a small bowl. Set aside.
Cream together sugar and butter until very light and fluffy, seven to nine minutes. Be sure to scrape down the sides of the bowl from time to time. Add 1/3 of the flour mixture, mix to combine, scrape down the bowl, then add half of the wet. Add another third of the dry, mix to combine, then add the remaining wet.
Toss the raspberries in the remaining third of the dry ingredients, then fold the contents of the bowl into the batter. Portion out the batter and bake 18-22 minutes, until the cupcakes spring back when pressed.
Remove cakes from pan and cool on a rack.
Swiss Meringue Buttercream
5 egg whites
1 c (200 g) sugar
2 sticks (226 g) butter, room temp
1 tsp lemon extract
Cook the egg whites and sugar in a small saucepan over medium heat, whisking constantly, until the sugar is completely dissolved (test by rubbing some between your fingers. If it's completely smooth, it's done). Pour into another bowl (a stand mixer is preferable) and whip on high speed until room temp. Then, on a medium-slow speed, add the butter, waiting until each piece is completely incorporated before adding the next. After all the butter has been added, turn the mixer back to high speed and whip until it has come together, about five minutes. Add the extract, beat briefly and then use.
If you have extra, store in the fridge for the next time you need to frost something.