Weigh the sourdough starter into a mixing bowl, add the plain flour, baking powder and eggs and whisk by hand.
Add the remainder of the ingredients and whisk to combine thoroughly, then cover and leave to stand for 1/2 hour
Fry the mushrooms in olive oil or butter.
Heat up a frying pan on a medium to high heat with butter or oil. Butter is certainly tastier and will give a better colour.
When hot, pour in the the batter to about 1/2 cm thick. Swirl the pan to get an even covering.
Add the mushrooms and they will partly sink in the batter. Cook for about 3 or 4 minutes.
When the top is no longer liquid, flip over and add the cheese topping (and ham if being used) and cook until the cheese is melted.