In a bowl, mix together the milk, egg yolks, butter, and vanilla. Combine the flour, baking soda, and baking powder and mix into the liquids until blended. Beat the egg whites and fold into the mixture.
Heat a heavy skillet until a drop of water bounces off the surface. Butter the skillet. Bake thin pancakes using 1/4 cup batter per cake until browned on both sides.
Spread with preserves, jam, or jelly, and whipped cream sweetened with powdered sugar. Fold into triangles and serve immediately. Makes 10 to 12 pancakes.