Preheat the oven to 350 degrees. Line a muffin tin with paper liners and set aside.
Sift together the flour, cocoa powder, baking powder, baking soda, and salt into a medium bowl. To a stand mixer with the paddle attachment, add the egg yolks and the sugar. Beat on high for two minutes until the mixture is thoroughly combined.
In another medium sized bowl, combine the melted butter, yogurt and vanilla. Using a rubber spatula, fold half of the butter mixture into the sugar and yolks. 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 attachment, beat the egg whites for one minute until foamy. Add the cream of tartar and turn on high. Beat the whites to the stiff peak stage. Fold the whites into the batter a third at a time being careful to keep as much air in the mixture as possible. Cover the bowl and let rest in the refrigerator for 30 minutes to allow the einkorn time to absorb the liquid and fat.
Divide the batter between the muffin cups and bake for 20-25 minutes until a toothpick inserted into the center comes out with a few moist crumbs. 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
The Greek yogurt in these cupcakes gives a decadent treat unexpected added protein. Score!