Mix the milk, mineral water, eggs and flour into a dough, leave to rest a little and then prepare 8 pancakes.
Chop the onion and roast in a little oil. Add the ham (finely chopped). Chop the celery and add to the pan as well. Squeeze in the garlic. Season with salt, pepper, oregano and parsley. Chop the mozzarella and add to the pan.
Spread the mixture over the pancakes and roll up. Brush a large baking dish with olive oil and place the pancakes in it. Mix the cream and mustard and pour over the pancakes. Cover and bake at 180 ° C for about 15 minutes.