Instructions

1. Combine the ground beef, breadcrumbs, egg, chopped onion, salt, pepper, nutmeg, and mustard. Gently knead the mixture until everything is well combined, being careful not to overmix to keep the meat tender.
2. Shape the mixture into 4-5 evenly-sized meatballs.
3. Roll each meatball in flour until lightly coated, shaking off any excess.
4. Place the coated meatballs in the fridge for 30 minutes. This helps
   bind the ingredients and prevents them from falling apart during cooking.
5. In a large skillet, heat the butter and oil. Add the meatballs and cook for about 10 minutes, turning regularly so they brown evenly on all sides. Keep the heat at a moderate level, allowing the meatballs to brown slowly. Try not to pierce them or they will lose their juices.
6. After browning, add 1½ cups of beef stock to the skillet. Cover with a lid and let the meatballs simmer for about 20 minutes, turning them occasionally.
   Using a meat thermometer ensures your meatballs are cooked through but still tender.
7. If the gravy needs thickening, you can mix in a little flour. And adjust the seasoning with salt and pepper to taste.