This recipe assumes you've already made or bought caramelized onions, but if you haven't, I used 10 medium yellow onions for this recipe, which resulted in about 150 grams of caramelized onions. I cook them extremely slowly in my dutch oven on the lowest flame my burner has. They are dressed with a little olive oil and 60 ml of water and allowed to sweat for as long as possible. I mix them up every 15 minutes or so until they are about 80% reduced, then I watch them carefully stirring often so they do not burn until they are reduced to 10% from starting volume. You can see my full guide to caramelizing onions here.
In a bowl add the pork, caramelized onions, breadcrumbs, garlic, egg, salt, red chili flakes, and smoked paprika and mix thoroughly with your hands. If it seems too wet, add some more breadcrumbs. Cover the bowl and place in the fridge for a half hour.
Pre-heat your oven to 180 degrees Celsius. Line a baking tray with parchment paper and make slightly larger than golf ball sized meatballs with your hands. Place them on the tray an inch or two apart. You should be able to get 16 meatballs out of this recipe.
Place in the oven for 20 minutes. At 20 minutes, turn them over and let cook for another 5 in the oven. While they are cooking, do step 5.
Take the dried ground mushrooms and put it in 60 ml of warm or room temperature water. In a sauce pan, make a roux of the butter and the flour. When it is combined, add the mushroom water and whisk. When the sauce thickens a bit, add the white wine and whisk some more. Slowly add the heavy cream and salt and pepper to taste. Use more or less heavy cream to your desired consistency.
When the meat balls are done, add them to the sauce pan and agitate the pan, coating the caramelized onion meatballs fully with the mushroom sauce. Serve hot and with bread.