Prepare the Batter: Mix flour and baking powder in a bowl. In a separate bowl, whisk together the egg yolks and milk until smooth. Combine with the flour mixture until just incorporated.

Beat the Egg Whites: Add cream of tartar to the egg whites and beat until frothy. Gradually add sugar while continuing to beat until stiff peaks form.

Fold and Cook: Fold one-third of the meringue into the yolk mixture until partially combined. Carefully fold in the remaining meringue until just blended. Heat a non-stick skillet over low heat, brush with butter, scoop about 1/4 cup of batter for each pancake, cover, and cook for about 5 minutes on each side.