Preheat the oven to 400 degrees F. In a small bowl, beat the egg with the flour, salt, to taste, and milk to make a smooth batter.
Butter a round ovenproof pie dish, then stir half the grated cheese into the batter, before pouring it into the dish.
Bake for 30 minutes. Take the dish out of the oven, sprinkle with the remaining cheese, and add the chorizo or pepperoni, if using, - or anything else - now, too. Return the dish to the oven and cook for another 2 or 3 minutes to make sure it's heated through.
Once the cheese on top is melted and looks burnished fold on the crustless pizza, take it out of the oven and serve, cut into slices. A green or tomato salad on the side would not be a bad idea...
Leftovers can be reheated the next day in a hot oven for 8 to10 minutes, but sadly they won't be as nice as the first time around.