Spiced Apple Filling:
In a saucepan, over medium-high heat, melt the butter. Add the sugar, cinnamon, nutmeg, and salt.
Stir to dissolve the sugar, about 3-5 minutes.
Add the apples, reduce heat to medium.
Cook the apples, stirring often, until tender, about 10 minutes. Set aside.
Preheat the oven to 200 F (95 C). This is to keep the cooked ebelskivers warm while you cook the others.
Combine the flour, sugar, baking powder, and salt in a large bowl.
In a small bowl, lightly whisk the egg yolks, then mix in the milk, melted butter, and vanilla extract.
Mix the wet ingredients with the dry ingredients with a wooden spoon until the mixture is smooth.
Beat the egg whites until stiff peaks form.
Gently fold the egg whites into the batter with a spatula.
The batter is ready to use.
Heat the ebelskiver pan over medium heat.
Grease the molds with melted butter or cooking spray.
When the pan is hot, add 1 tablespoon (15 ml) of batter to each mold.
Add 1 teaspoon (5 ml) of spiced apple filling to the center of the batter, then cover with another tablespoon (15 ml) of batter.
Cook until the bottom of the ebelskivers is lightly golden and crispy, about 3-5 minutes. Use 2 wooden skewers to flip the ebelskivers and cook until they are lightly golden on the second side, about 3 minutes more.
Place on a plate and serve, dust with powdered sugar.