Combine bread crumbs and milk in a small bowl. Let set aside for 10 minutes.
In a large mixing bowl, combine the soaked bread crumbs, ground chicken, onion, garlic and parsley. Season generously with salt and black pepper and mix them well. Shape them into meatballs.
Heat a large frying pan over medium-high heat. Drizzle in a little olive oil and heat until the oil is slightly shimmering. Turn the heat down to medium-low and add in the meatballs in a single layer. Sear the meatballs until both sides are well-browned. Do this in batches if your pan is too small, adding more oil if necessary and watching the heat. Transfer the meatballs into a baking dish.
Using the same frying pan, add in the mushrooms and cook over medium heat until the mushrooms have reduced in size and are soft. Transfer the mushrooms into the baking dish with the meatballs, leaving the mushroom juices in the pan.
Preheat the oven to 200 degrees Celsius.
Heat the mushroom juices until it starts to simmer. Add in the flour and cook for 1 minute. Add in the chicken stock and bring it to a simmer. Add in the cream and milk and bring it to a simmer. Season with salt and black pepper. Taste and adjust the seasonings if needed.