Mix the minced beef and pork in a bowl and stir well. Add onion, garlic, breadcrumbs, and egg to the mixture. Add milk and season with salt and pepper.

Make small round balls from the mixture. Place them all on a clean plate and refrigerate for 2 hours. This helps the dough hold its shape during frying.

Add oil to a large heavy-bottomed pan and set it to medium heat. When the pan is hot, add the meatballs and sear them on all sides.

Once seared, place them in an ovenproof dish with a lid. Then, bake them for 30 minutes at 180 degrees Celsius (356 degrees Fahrenheit) (conventional oven) or 160 degrees Celsius (320 degrees Fahrenheit) (fan oven).

The sauce is a roux-based sauce: Start by melting the butter and adding the flour while whisking vigorously to avoid lumps. This takes a few minutes, so the flour can cook through. Add both stocks while continuously whisking lightly. Then add the heavy cream, soy sauce, and Dijon mustard. Lower the heat and let it simmer until it thickens, whisking less and less frequently.

Serve the dish with your favorite potatoes - either mashed potatoes or boiled potatoes. Enjoy your meal.