Mix together flour, yeast and salt. Make a well in the centres and pour in liquids. Draw the flour into the liquid to make a soft dough.
Knead dough on oiled surface for about 5 minutes. Place in bowl, cover with damp cloth and leave in a warm room until doubled in size (about 1 – 2 hrs). Knock back and knead again for about 10 minutes and allow to rise again in a warm place under cover of a damp cloth.
Remove dough from bowl and wrap in Clingfilm and store in fridge or freezer. Make sure you put it in the coldest part of the fridge or it will continue to rise. Last time I made this I had a full fridge and put the dough in the top of the door. Only to have the fridge door seemingly open by itself an hour later as the dough had expanded to such an extent the pressure made holes in the Clingfilm and opened the door. It was like a scene from the 50's horror film the Blob.
When ready to use roll out the dough and cut into 2 inch circles using a round cookie cutter. Lay circles onto a baking tray and allow to rise again for about an hour.
Meat topping: fry the onions in a little olive oil until translucent and transfer to a large bowl. Fry the mushrooms in a little olive oil until any water has evaporated and add to the bowl with the onions. Then fry the meat in a little olive oil until just cooked through. If you are using ground beef rather than a flavoured sausage meat you will need to season it at this stage to your taste. Add the just cooked meat to the bowl and combine well with the onions and mushrooms. Store in the fridge until ready to use.
To make up the pizzas: Spread the passata or bolognese sauce over the top of the pizzas. Sprinkle on the meat mixture. Add 3-5 bits of diced mozzarella and top with grated cheddar.
Bake in centre of the oven at about 175 for 15 - 25 minutes or until the cheese has melted. Serve warm