Directions:
1. In a bowl, whisk together the flour, baking powder, salt, and sugar. In another bowl, lightly whisk the egg yolks, then whisk in the milk and the 4 tablespoons of melted butter. Whisk the yolk mixture into the flour mixture until well combined; the batter will be lumpy.
2. In another bowl, using an electric mixer, beat the egg whites on high speed until stiff but not dry peaks from, 2 to 3 minutes. Using a rubber spatula, gently fold the whites into the batter in two additions.
3. Heat the pancake puff pan over medium high heat. With a pastry brush, coat each well of the pan with butter. When the butter bubbles, pour 1 Tablespoon of batter into each well. Put 1 teaspoon of filling in the center of each pancake and top with 1 Tablespoon of batter. Warning: do not let out the dog, pour someone a glass of milk, or change your facebook status, stay at the stove. Cook until the bottoms are golden brown and crispy, 2-4 minutes. Using 2 wooden skewers or 2 mini spatulas, flip the pancakes over and cook until the other side is golden and crispy, about 3 minutes more.
4. Transfer cooked pancake puffs to a plate. Dust with powdered sugar if desired. Repeat with remaining batter and fillings. Can be served with syrup or whipped cream.
5. Serve immediately. Makes about 40.