In a large bowl, whisk together flour, sugar, baking powder & salt.
Separate eggs, set whites aside.
Whisk in egg yolks, buttermilk, melted butter and vanilla extract. Whisk until smooth & thoroughly mixed - some lumps will remain.
In a separate bowl, using electric mixers, beat egg whites until stiff peaks form.
Fold whites into batter.
Grease each well of the mold with oil or softened butter using a pastry brush or paper towel.
Heat pan up over medium heat.
Pour batter into each well, filling about half way. I use a small ladle.
Fill with about half a teaspoon of jam or a pinch of chocolate chips.
Top with additional batter - I fill 1/8" from the top.
Cook until bottoms are golden and sides are set, about 3-4 minutes, then, using your method of choice, flip pancakes and continue to cook until bottom is golden - another 2-3 minutes. I use 2 chopsticks to maneuver and flip each ebelskiver. I also do a "3-point turn" when I flip them. Whatever works for you.
Repeat with remaining batter.
Remove each pancake and serve with a dusting of powdered sugar or syrups. Enjoy.