01 - Set oven to 400°F and line a baking sheet with parchment paper.
02 - In a large bowl, combine ground turkey, breadcrumbs, egg, milk, parsley, grated onion, garlic, salt, and black pepper; mix gently until just incorporated.
03 - Shape mixture into 20 to 24 small meatballs and place on the prepared baking sheet. Bake for 15 to 18 minutes until golden and cooked through.
04 - While meatballs bake, bring a large pot of salted water to a boil. Cook egg noodles according to package directions, then drain and set aside.
05 - Heat olive oil and butter in a large skillet over medium heat. Add mushrooms and sauté until browned, about 5 to 6 minutes. Add diced onion and cook until softened, 2 to 3 minutes. Stir in garlic and cook for 1 minute.
06 - Sprinkle flour over vegetables and stir constantly for 1 minute to eliminate raw flour taste. Gradually whisk in chicken broth. Add Worcestershire sauce and Dijon mustard, bring to a boil, then reduce heat and simmer until thickened, about 5 minutes.
07 - Lower heat, stir in sour cream until smooth. Season with salt and black pepper to taste.
08 - Add baked meatballs to the sauce and simmer gently for 3 to 4 minutes to heat through.
09 - Serve meatballs and sauce over cooked egg noodles and garnish with chopped fresh parsley.