In a large bowl, whisk the dry ingredients together. Begin preheating the pan on the stovetop.
Separate the eggs into two separate bowls. The whites will end up being beaten separately. The yolks will be beaten with the other wet ingredients.
Beat the yolks with the butter and buttermilk. Beat the egg whites until they just hold a 2 inch peak. Do not overbeat them. Add the yolk-butter-buttermilk mixture to the dry ingredients in a slow steady stream while mixing gently with a rubber spatula. Don't worry if there are still dry patches. Just don't over mix. Fold in the egg whites gently. If the batter seems too thick to be able to flow like molten lava, add a splash more buttermilk and mix in gently. It should be less firm than drop cookies, but more than the usual pancake batter.
Fill the hollows of the greased hot pan and cook the aebleskiver until they are brown and a skewer poked into them comes out clean. (See below for more detail on this process). If you are not having your diners come up and retrieve them as they get done, let cooked skivvers rest in a 200 degree oven until the whole pile is cooked.
MORE COOKING TIPS:.
I have a glass-top range, which works with this pan, as it has extra cast iron at the bottom of the cups making it flatbottomed. (An antique pan designed for a gas range might have spherical bottoms, which might not have enough contact with the glass top.).
I brushed the cups with a little canola oil, and then preheat the pan until a drop of water danced when flicked into one of the cups, but when cooking I turned the heat down a bit lower than I would use for something less thick. More into the medium range. I found in the course of cooking my batch, that you don't want to fill the cups more than 1/2 to 2/3 full, because they will expand as they cook. It is easier to work with about 3 of the holes at a time, at least at my expertise level of making skivvers. So fill batter in three cups, let it cook and firm up a little bit on the bottom, then drop in the chunk of apple or whatever filling you want to use (just a little 1/2 inch chunk of something), and get it pretty close to where it's ready to turn before starting the next group of 2 or 3 holes. Once those are full, go back to the first group and spin the balls a quarter turn so that at the top you see raw along one half and cooked along the other. I was not able to do this first turn with the wooden skewer - I used a teaspoon, being careful of the nonstick finish which is very minimal. I would not recommend the As Seen on TV pan to someone who was not able to cook with lower quality pans, as it is going to stick if you don't know what you are doing, and that nonstick finish is going to disappear with even the slightest level of abuse. Part of knowing what you are doing is to let it cook enough before you try to turn it. Just like a cake, it will start to pull away from the edges of the cup. Watch for that and then GENTLY probe and feel with the edge of the spoon whether it will allow you to lift the bottom of the ball, whether it is ready to come away. This is why lower heat is key - if the heat is too high, you are not going to have time to deal with the transition between raw and sticking, ready to turn, and burnt and sticking. The first turn is the hardest. After that, you can do the other two quarters with the wooden skewer. You can roll it around in the cup more than just three times if that's what you want. Be sure to brush the cups with more oil before refilling with batter. Without the oil, it is going to stick. It's harder to explain than it is to do.
Also, when it is time to clean up, after the pan has cooled, use a brush (like a toothbrush) or plastic scrubby to GENTLY rub off any bits sticking to the pan and just rinse under very hot water. Do not use soap. It's just like taking care of a wok. Towel it dry. Put a dab of oil on a paper towel and wipe the slightly-oily towel in the inside of those cups. Put on the burner so that the sheen of oil is absorbed. Let it cool, and wipe down with a clean paper towel. Make sure there is no dampness left - don't let it air dry.
Just for a little more geekery - Japanese takoyaki, Thai kanom krok, Indian paniyaram, and Dutch poffertjes are similar food technology.