Fry the meatballs in a little oil until brown on the outside but still a little pink within - they are getting baked so don't need to be cooked through at this stage.
Take a walnut sized piece of dough and pat it out to make a thin disk and scatter with a handful of mozzarella. Place a meatball in the middle and bring the dough up around it, squeezing together to seal in the filling.
Pour passata, white wine, olive oil, garlic powder, oregano and sea salt into an oven proof dish and place the dough balls around it on a baking tray. Brush these with the herb butter.
Bake for 20 minutes until the dough has risen and the sauce is bubbling.