Preheat the Ebelskiver pan on medium-low heat and put a dab of butter in each well to melt.
Melt 3 Tbsp. of butter or coconut oil and set aside for a few minutes to cool. Add 1 tsp. of vanilla and 1 tsp. of baking soda, if using. Add this mixture to your fermented batter and mix until incorporated.**
Fill each well of your pan about 3/4 full with batter. Do not overfill.
If you're going to use an inclusion like spiced apples, chocolate chips, or sausage, do it now. 1-2 tsp. of anything should be enough to give flavor but not overfill the well of the pan.
Cook until the batter begins to buble and the underside becomes stiff.
Using a bamboo skewer or knitting needle, carefully turn the pancake over so that what was on the top is now on the bottom.
Bake a further 3-5 minutes or until golden browned. If you've included a filling, allow a little more time.
Plate and cover and serve hot.