Preheat the oven to 350 degrees. Line a muffin tin with paper liners and set aside.
Sift together the flour, baking powder and salt into a medium bowl. Add the egg yolks and the sugar to a stand mixer with the paddle attachment and beat on high for 2 minutes until the mixture begins to thicken.
In another medium-sized bowl, combine the melted butter, yogurt and vanilla. Using a rubber spatula, fold in half of the flour mixture. When completely moistened, add half the butter mixture. Repeat these steps using all the flour and butter mixtures. Transfer to a large bowl. Wash and dry the mixer bowl. It must be clean and dry to whip the egg whites.
Reattach the clean and dry bowl to the mixer. Using the whisk, beat the egg whites for one minute until foamy. Add the cream of tartar and turn on high. Beat the whites till stiff peaks form. Fold the whites into the batter 1/3 at a time, being careful to keep as much air in the mixture as possible.
Divide the batter between the muffin cups and bake for 20–25 minutes until a toothpick inserted into the center comes out clean.
Transfer the cupcakes to a rack and let cool for 10 minutes. Remove from the pan and let cool completely about 1 hour.
One Last Thing
What’s the difference between white and yellow cupcake batter? Yellow cake all about using egg whites AND the yolks too!