This Danish treat is essentially a pancake ball. They often had fillings like jams or applesauce but we always made them plain and dipped them in powdered sugar.
Mix flour, sugar, baking powder, and salt together in a second bowl. Mix in egg yolks, condensed milk, and shortening. Fold in egg whites.
Heat an aebleskiver pan over medium heat until hot. Brush each cup with a little melted butter using a pastry brush, then fill each with about 2 tablespoons of batter until almost full. Cook until they begin to bubble; flip over, allowing batter to fill the bottoms of the cups. Continue to cook, turning as needed, until golden brown. Repeat with remaining batter.