1. Mix the beef and pork together with your fingers, add the onions, garlic, breadcrumbs, egg, milk, and season.
2. Shape small meatballs from the mixture with your fingers and let them rest in the refrigerator for at least 2 hours.
3. In a frying pan over medium heat, pour a little oil and then fry the meatballs until they have a nice golden color.
4. Once your meatballs are nicely browned, place them in an oven-safe dish and continue cooking for 30 minutes at 160 or 180 degrees Celsius.
5. For the sauce, melt the butter in a saucepan, add the flour and stir for 2 minutes. Add the vegetable and beef broths while continuing to stir. Then add the cream, soy sauce, Worcestershire sauce, and Dijon mustard, and increase the heat to thicken the sauce.
6. When everything is ready, serve your meatballs with your favorite potatoes (mashed, fried, or boiled).