Got an ebelskiver pan for xmas, so this was my first attempt at making them. They're small filled pancakes, so I put a nice little glob of Nutella inside. You have to work pretty fast, or turn the fire down really low so the bottom doesn't over cook while you're adding the filling and covering it with extra batter. Flipping it can be tricky too. The pan came with these strange wooden tongs made specifically for the job, but I think chopsticks would have worked just as well.
Here's the base recipe from Ebelskivers, by Kevin Crafts
1 cup all-purpose flour
1.5 tsp sugar
1/2 tsp baking powder
1/4 tsp salt
2 eggs, separated
1 cup milk
2 Tbsp melted butter, slightly cooled
Whisk together flour, sugar, baking powder and salt.
In a small bowl, whisk the egg yolks, then whish in the milk and melted butter.
Add the yolk mixture to the flour mixture and stir till blended. The batter will be lumpy.
In another bowl, beat the egg whites till still but not dry, peaks form. Fold about 1/3 of the egg white into the batter to lighten it. Then fold in the rest till no white streaks remain. Use the batter right away.
I recommend heating your pan up first, then turning the first as low as possible. Have your batter in a pourable container, so you can get it out quick. Originally I tried spooning it into the slots, but it took too long. Once you've filled each slot, put a glob of nutella in the center of each, then quickly cover it with more batter. At this point you can turn your fire back up to med.