In a large bowl, whisk together flour, sugar, baking powder and salt.
Separate eggs, set whites aside.
Whisk egg yolks, buttermilk, melted butter and vanilla extract into the flour mixture. Whisk until thoroughly mixed.
In a separate bowl, using an electric mixer, beat egg whites until STIFF peaks form.
Fold stiff egg whites into batter.
Grease each well of the Ebelskiver pan with cooking spray or melted butter.
Heat pan on stovetop over medium heat.
Ladle batter into each well, filling halfway.
Drop in about 1/2 tsp of whatever fillings you desire, such as a few blueberries, cherries, chocolate chips or 1/2 tsp of any jam.
Top the added filling with additional batter to fill mold to about 1/8 in. from the top.
Cook unti the bottom is golden and sides are set. (This takes several minutes.)
Use two chopsticks to turn the dough ball over completely to cook the other side for several minutes until the entire ball is golden brown.
Remove from the pan and dust with powdered sugar before serving.