Tear the bun into small pieces, add to the food processor along with the chopped onion and pulse until crumbly and moist.
Add the ground meat, salt and pepper and pulse a few times until the ingredients are well incorporated (but do not overprocess).
Form good size meatballs and set aside.
In a large shallow dish melt the butter, add the flour and whisk until smooth. Add the wine, some of the milk and continue whisking until the mixture thickens. Gradually add the rest of the milk, stock, mustard and garlic granules and cook until the sauce thickens whisking all the time. Whisk in the fromage frais and adjust the seasoning if needed.
Place the meatballs in the sauce (without overlapping one another), cover and simmer for about 15 minutes or until the meatballs are fully cooked, turning a couple of times. Remove from the heat and serve immediately.
Use either turkey, pork, chicken or beef but ensure it's not too lean (I recommend 7% fat content).
I recommend using a food processor to prepare the meatballs. The mixture is ready in seconds and your meatballs will be super soft (softer than if you were preparing it with our hands). Also the onion and bread need to be turned into a crumbly, moist mixture and this is best done in a food processor.
I made my meatballs quite large to make sure they wouldn't be squashed together in my dish (they must not overlap one another). But you can make them a little smaller if using a very large dish if you prefer.
You can use low fat creme fraiche or sour cream instead of the fromage frais in the sauce.
You can prepare the meatballs 2-3 hours in advance but I do not recommend making them too far in advance. I find that raw onion can often affect the flavour of the meat if left uncooked for too long.
Best served immediately. Leftovers can be refrigerated for up to 3 days.
Freeze individual portions in an airtight container for up to 3 months.