Preheat the oven to 450 F or turn the broiler on high. In a large bowl, mix together the ground beef, dill, whole grain mustard, garlic powder, egg, buttermilk, and bread crumbs until totally combined. Roll the into individual balls.
Arrange the meatballs on a baking sheet lined with foil or greased with cooking spray. Bake for 20 minutes, flipping once.
While the meatballs cook, melt the butter in a Dutch oven over medium high heat. Let the butter brown and foam.
When the butter stops sizzling, add the sliced mushrooms. Stir the mushrooms occasionally. As they release their moisture, add the onions, garlic, tomato paste and Worcestershire sauce. Season with salt and pepper, to taste.
Stir in the dry gemelli pasta (or pasta of choice). Pour in the beef broth and water. Bring to a rolling bubble.
Add the cooked meatballs to the soup. Reduce the temperature to a simmer. Cover and let cook on a medium low temperature for 20-30 minutes.
Stir in the Greek yogurt and parsley. Season with salt and pepper, to taste. Serve hot alongside a roll of crusty bread, for soaking up the soup. Enjoy!