Preheat the oven to 400 degree F and line a large rimmed baking sheet with foil. Place a skillet over medium heat and melt the butter in it. When the butter has melted, add the grated onions and saute for 3-4 minutes, until soft.
In a large bowl, mix the sausage, ground beef, panko, 1/2 cup apple butter, sour cream, eggs, salt, pepper, and allspice. Add the onion, once it cools. Get your hands in it and mix well, until evenly combined.
Measure out the meatballs into one ounce portions. Roll tight balls and place them on the baking sheet, close together, but not touching. You should have 40-45 meatballs.
Bake for 15 minutes. Meanwhile, mix the remaining 1/2 cup of apple butter, with beef broth, honey, and 1-2 dashes of cayenne pepper. Whisk well.
After 15 minutes, remove the meatballs from the oven. Pour the sauce over the top, making sure to cover each meatball, and place back in the oven for 5-7 minutes.
Once cooked through, shake the baking sheet a little to loosen the meatballs and serve warm.