In a bowl, combine ground beef, breadcrumbs, milk, Worcestershire sauce, salt and pepper. Mix thoroughly.
Portion the meat evenly into bite sized pieces. Using your hands, shape the meat into balls. (Dampen your hands with water to prevent meat from sticking to your hands.)
Heat a non-stick pan over medium heat. Add the meatballs and onions to the pan. Sear the meatballs on both sides until nicely charred for approximately 2 to 3 minutes per side.
Then add in the broth, cover with a lid, and bring to a low simmer for 10 to 12 minutes.
Meanwhile, mix the flour in a bowl with a little water at a time. Whisk until a smooth paste is formed. Make sure there are no lumps.
Add the flour/water mixture to the broth a little at a time while stirring until the sauce starts to thicken. (Sauce consistency should coat the back of a spoon.) Once thickened, whisk in the sour cream and simmer for 4 to 5 minutes longer. Taste and adjust the seasoning with salt and pepper if needed.
Serve with bread.