To a large pot, add 4 quarts water and begin heating while you prepare the ingredients. Peel and dice the onion into 1/4" chunks, mince the garlic and parsley for both the meatballs and the gravy, and carefully break the noodles into even pieces, about 2" long. Make the breadcrumbs by drying 2 medium slices of bread in the oven at 150 C. with the door open partially for 15 min, or until dehydrated and crispy. Place in a Ziploc bag, remove air and seal, and crush with a rolling pin. You should have about 1/2 C. breadcrumbs.
In a large, heavy-bottomed saucepan or deep skillet, add 1 tbsp. butter and the onion. Saute until golden and translucent; add to a heatproof medium-sized mixing bowl.To the bowl, add the remaining meatball ingredients, and with your hands, knead together and form into 16 even balls, approx. 1 1/2" in diameter.
In the same skillet used to saute the onion, add the remaining tbsp. butter and, when hot, add the meatballs in a single layer. Cover the pan and cook, shaking the balls occasionally to brown evenly and avoid sticking. When done, remove the meatballs to a plate.
Using the same pan from the meatballs, heat 1/4 C. (4 tbsp) salted butter, then add 1/4 C. flour and the minced garlic. Fry for about 2 minutes, or until golden and fragrant without overcooking the garlic. Pour the milk in a steady stream, whisking continuously until fully incorporated. Bring to a boil, cook for a few minutes until the gravy coats the back of a spoon, and remove from the heat. Add the salt, pepper, and parsley.
To the 4 quarts boiling water, add the broken noodles and 1 tbsp. butter, if you wish, to deter foaming over. Cook until desired doneness, then drain the water. Add the gravy and stir to coat the noodles and prevent sticking together.