Dissolve the stock cube in 50 ml (¼ cup) of hot water.
Combine bread crumbs, milk, whipping cream, eggs, pepper, and the dissolved stock cube in a bowl. Mix everything together and allow it to soak for 10 minutes.
Grate the onion and combine it with minced meat, Dijon mustard, and the bread crumb/egg mixture. Use a wooden spoon or clean hands to stir everything together until well combined.
Before shaping all the meatballs, fry a small portion of the mixture and taste it to determine if you need to add more salt or pepper. This allows you to adjust the seasoning according to your preference before proceeding.
Moisten your hands with cold water and shape the meat mixture into tablespoon-sized meatballs.
Put the meatballs on a baking sheet that has been lined with parchment paper.
Bake the meatballs for 6 to 8 minutes.
Remove the meatballs from the oven and transfer them to a frying pan. Fry the meatballs in butter until they are nicely browned.
Notes
You can expect to make around 60 meatballs with this recipe.