Combine the ground turkey, egg, onion, breadcrumbs and garlic. Form into 10-12 even sized meatball. Place in 8x8 glass dish and bake at 375 ℉ for 20 minutes.
Add water to a large pot and heat to boiling to cook the egg noodles.
In a large deep skillet, heat butter and olive oil. Add onions, mushrooms and bell pepper and sauté over medium heat 10 minutes until softened. Add garlic and sauté for one minute.
Add chicken stock, mustard, half & half, and sour cream to a measuring cup or bowl. Stir to thoroughly combine and set aside.
Reduce heat to low and add flour to the skillet. Stir for one minute.
Stir in the liquid mixture and simmer as the sauce thickens, about 5 minutes.
Once the egg noodles are cooked, strain and set aside. Save a quarter cup of the pasta water.
Add meatballs to sauce, simmer for a few minutes, and stir until mixture is combined and heated through. Add a Tbsp of pasta water at a time to thin the sauce if needed. The goal is a thick, smooth sauce that coats the meatballs. Season to taste with salt and pepper.
Sprinkle with fresh parsley and serve over egg noodles.