2 cups all-purpose flour
3/4 tsp baking soda
3/4 cup unsalted butter, room temperature
2 cups sugar
2 tsp lemon juice or extract
6 large eggs, separated, room temperature (best separated when cold)
3/4 cup plain, full-fat yogurt
2 tablespoons pure vanilla extract
1/2 tsp almond extract
Preheat oven to 350 F. Prepare three 6" pans with parchment paper and set aside.
Cream butter, half of sugar, and lemon juice/extract in mixer until very pale and fluffy (about 5 minutes). Add egg yolks, one by one, scraping sides of bowl after each addition. Add extracts, mix well.
Sift dry ingredients together and add to creamed mixture on low speed until just incorporated. Add yogurt on low speed.
Transfer to another bowl, clean mixer bowl and wipe with vinegar or lemon juice on paper towel, to eliminate any trace of grease. Whip room temperature egg whites and remaining sugar until stiff peaks form (about 10 minutes).
Fold into cake batter gently. Pour batter into prepared cake pans and bake until inserted skewer comes clean. Let cool for 20 minutes in pan, then invert onto cooling rack until completely cool.
Makes one 3-layer, 6" cake.