Pre-heat oven to 200ºC (180ºC Fan). In a large mixing bowl, combine all meatball ingredients. Using your hands mix all the ingredients together really well, squeezing and mashing the mince so everything is nicely combined. Roughly divide the mixture into around 16 – 18 golf ball-sized balls.
In a medium pan over medium heat, add your meatballs, in batches if needed, and brown until golden, about 6 to 8 minutes. Set aside. In the same pan, add 1tbsp sunflower oil. Add your onions, garlic, and mushrooms and allow to sweat down, about five minutes.
Continue cooking until ingredients begin to caramelise, a further three minutes, then add your white wine. Allow the wine to bubble and reduce for about two minutes. Add lamb stock and allow it to reduce, for a further five minutes. Add your cream, and cep powder if using, and stir vigorously to fully incorporate. Remove from heat.
In an ovenproof baking dish, add your meatballs and cover with your cream sauce. Bake in the oven for 30 minutes. Serve with fresh, toasted sourdough.