Pour the milk over the breadcrumbs. Combine all the ingredients together, except for the oil. Mix to combine.
Shape into meatballs, about 1 Tablespoon each. I like them on the smaller side, so this will make about 50 meatballs.
Heat 1 1/2 – 2 Tablespoons oil into a heavy bottomed skillet or dutch oven. Cook the meatballs in two batches, until they are golden brown on both sides. They don’t have to be cooked through all the way at this point, since they will finish cooking in the sauce. Set the meatballs aside.
Remove most of the oil, except for about 1 1/2 Tablespoons.
Add the onion, season with salt and ground black pepper. Cook for about 3 minutes.
Add the mushrooms and garlic. Season with salt and ground black pepper. Cook for about 8 minutes, until the mushrooms are golden brown. At first, the mushrooms will exude a lot of liquid, so use a wooden spoon to scrape up all the browned bits left from the meatballs and onions. Then when the liquid evaporates, the mushrooms will get golden.
Add the flour, mix to combine until all of the flour is incorporated into the mushrooms. If your skillet is dry, add a little bit of butter or oil, enough to coat all of the flour.
Gradually pour in the white wine and chicken broth, (if you’d rather not use wine, just omit it) using a whisk to mix, which will prevent lumps from forming. Reduce the sauce to a simmer and cook until it thickens up, about 5 minutes.
Add the sour cream and the heavy cream, whisking until smooth. Add the meatballs to the gravy and continue simmering for another 5 minutes or so, just until the meatballs are completely cooked through.
Garnish with fresh herbs, such as parsley and/or dill.