In a large bowl, mix together all of the meatball ingredients until fully combined. You can knead it with your hands or mix it in a stand mixture with a dough hook attachment.
Form balls with the meat mixture with your hands or a cookie scoop. Place the meatballs on a baking sheet and place in the freezer for 5 - 10 minutes.
Heat some oil on a large skillet. Brown the meatballs on all sides until the meatballs are cooked through. Remove from the saucepan and set aside.
Melt the butter on the skillet. Whisk in the flour until medium brown. Pour in the broth and simmer until thickened. Add in the milk and mustard. Simmer until thick and creamy.
Place the meatballs in the sauce and cook until the meatballs are heated through.