Step 1

Preheat oven to 350ºF. Line 15 standard muffin cups with paper liners.

Step 2

Place egg whites in stand mixer with whisk attachment and beat on medium speed until white and foamy. With mixer running, slowly pour in 1/4 cup (50 g) of the sugar and continue beating on medium-high until medium-stiff peaks form. Scrape the beaten whites into a bowl and set aside. Wipe out mixer bowl and dry.

Step 3

Measure flour, remaining sugar, baking powder and salt into the mixer bowl. Switch to paddle attachment and beat the dry ingredients on medium speed for 1 minute (this replaces sifting and thoroughly combines).

Step 4

Toss in the chunks of soft butter. The mixture will go from lumps of butter, to coarse crumbs, to one cohesive lump of dough. When it comes together in that lump, set timer for 4 minutes and beat on medium until light and fluffy. **If the texture remains like sandy crumbs instead of coming together into a cohesive ball of dough, this means your butter isn't soft/warm enough. Simply soak a dishtowel with hot water and hold it on the bottom of the mixer bowl as it beats. Repeat as the towel cools until the dough comes together. It won't take long.

Step 5

Add egg yolks to creamed butter mixture and beat on medium, pausing to scrape down sides and paddle, until combined.

Step 6

Reduce mixer speed to low and drizzle in the milk and vanilla. Right away scrape down the sides of bowl and paddle, then beat on medium-low, pausing to scrape down sides and paddle again once or twice, until the batter has no more big lumps - 40-60 seconds in total. The batter will look fluffier but curdled, with tiny lumps uniformly through the batter.

Step 7

Remove bowl from stand mixer and use a large spatula to fold 1/3 of the beaten egg whites into the batter. (This lightens the batter making it easier to gently incorporate the rest.) Gently fold in remaining egg whites until no white streaks remain.

Step 8

Portion batter into muffin cups (about 1/3 cup batter per cupcake) and bake for 18-22 minutes, rotating pans once around 14 minutes. They should be around 190ºF internal temperature. They will not necessarily be golden on top when done. Cool completely on wire racks before frosting.