Preheat the oven to 200°C/400°F/gas mark 6. Fry the mushrooms in a knob of butter until tender and any liquid has evaporated.
Knock back the risen dough and divide into two equal pieces. Shape each piece into a ball then roll out on a floured surface into a large circle, about 27cm/10.5 inches wide. Place each pizza on a baking sheet lined with baking parchment.