This buttercream is the bomb.

INGREDIENTS

Cupcakes
1 1/4 cups cake flour
3/4 teaspoons baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
2 eggs
1 cup sugar
1 1/2 teaspoons pure vanilla
1/2 cup canola oil
1/3 cup milk
1/3 cup sour cream

Buttercream
1/2 cup granulated sugar
2 large egg whites
1/2 cup unsalted butter, room temp cut into 6 pieces
1/2 tsp vanilla
pinch kosher salt

DIRECTIONS

Preheat oven to 350*F.

In a medium bowl, add cake flour, baking powder, baking soda and salt.  Stir together with whisk, and set aside.

In the bowl of an electric mixer, add eggs and beat 10-20 seconds.  Add sugar and continue to beat on medium speed about 30 seconds.  Add vanilla and oil, beat.

Reduce mixer speed to low and slowly add about half of the flour mixture.  Add the milk, then the rest of the flour and the sour cream.  Beat until just combined.  Scrap down the side of the bowl.

The batter will be thin.   Pour batter into a muffin pan prepared with paper liners.  Fill liners about 2/3 full.

Bake cupcakes in pre-heated oven for 12-14 minutes. Cool then Frost.

Buttercream: In a small heatproof bowl, whisk the sugar and egg whites. In a 1-quart saucepan, bring 2 cups of water to a simmer over medium-high heat. Set the bowl over the simmering water (don’t let the bowl touch the water) and heat the mixture, whisking occasionally, until hot to the touch, 4 to 6 minutes. It will thin out a bit as the sugar melts.

Remove the bowl from the heat and scrape the mixture into the bowl of a stand mixer fitted with the whisk attachment. Whip on medium-high speed until the mixture is light, white, and cool to the touch, 4 to 6 minutes. Reduce the speed to low and add the chunks of butter one at a time. Increase the mixer speed to medium and beat until the buttercream is smooth, 4 to 5 minutes. Mix in the vanilla and salt.

I got the cupcake recipe here.