In a medium-sized bowl, beat the egg whites with an electric mixer until stiff peaks form. Set aside.
Mix together the flour, baking powder, salt, baking soda, sugar, egg yolks, 4 Tbsp. melted butter and buttermilk and beat until smooth.
Gently fold in the egg whites last.
Using a pastry brush, brush the bottom of each aebleskiver pan cup with melted butter and heat over medium heat until hot.
Pour in about 2 tablespoons of the batter into each cup. As soon as they get bubbly around the edge, flip them over (In Denmark they typically use a knitting needle to flip, but you can use a chopstick or a fork).
Continue cooking, turning the ball until is is golden brown all the way around and is cooked through (like a pancake). It might take a couple tries to get the feel for it, but once you do you will be flippin' aebleskiver like it's nobody's business!
Serve with jam or syrup and sprinkle with powdered sugar.
Video
Notes
Nutrition does not represent powdered sugar, jam, or other toppings.