1 tablespoon baking powder (aluminum-free, please)
1 teaspoon kosher salt
10 tablespoons unsalted butter, at room temperature
1 cup granulated sugar, divided
2 teaspoons clear imitation vanilla extract*
2/3 cup whole milk
4 egg whites
Preheat oven to 350˚F. Butter an 8-inch, fairly deep cake pan on bottom and sides.
In a medium bowl, whisk together flour, baking powder and salt; set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat butter and 1/2 cup of the sugar together until light and fluffy, 4 minutes. Add vanilla and beat again until incorporated. Scrape down sides of the bowl and beat a few seconds more if ingredients need further incorporation.
With the mixer on low, add flour mixture and milk in two parts each, alternating between the two (flour, milk, flour, milk), stirring just until each addition is incorporated and scraping down the sides bowl as needed. Set aside for a second.
In a very clean, large bowl using an electric mixer…
…beat the egg whites until frothy. Add the remaining 1/2 cup sugar a tablespoon at a time while you continue beating, allowing the sugar to incorporate each time before adding more. Beat until stiff peaks form.
Add about a 1/2 cup of egg white mixture to your batter and fold in, working gently but with purpose, to lighten the batter. Add the rest of the egg white mixture and fold in – again, really working with care, this isn’t a race – gently but firmly, making each stroke count, until the batter is homogenous. This is not that easy; it’s a thick batter, so you may feel like it’s taking forever, but right after you feel that way, suddenly your batter will go from two distinct batters to one really great, fluffy one. Be patient.
Pour carefully into the prepared cake pan and smooth the top without pressing down – don’t want to deflate all that hard work. Bake for 25 to 30 minutes until cake tester comes out clean or with a few crumbs clinging to it. Check after the 20-minute mark, and continue to do so as it finishes up: you want a moist cake, not a dry one.
Remove and allow to cool completely in pan. Flip over to remove it – this cake is so amazing that it just glides right out of the pan – and right it on a cake plate. Do whatever you want with it, but I say you just eat it.