Combine flour, sugar, and baking powder in a mixing bowl.
Mix together milk, cooled butter, vanilla, and yolks.
Whip egg whites with cream of tartar until stiff peaks form.
Add liquid mixture to dry mixture, stirring just to combine (do not over beat or gluten will form and pancakes will be tough). Fold in the whipped egg whites.
Heat a greased non-stick skillet. Spray the inside of eight round ring molds with oil and place two in the skillet. Fill each ring mold with batter to the half-way mark. Place a lid on the pan and cook on medium heat for five minutes. Remove lid and using a spatula, flip each mold, being careful not to spill batter contents. Once flipped, return lid and turn heat to low. Continue cooking another four minutes. Using spatula, remove filled ring molds to wire rack and carefully remove fluffy pancake. Repeat with remaining batter; serve with blackberries and syrup (if desired).