Heat 1 tbsp olive oil in a large frying pan. Add 200g (7oz) torn shiitake mushrooms and 100g (3½oz) each of sliced portobello mushrooms and forestière mushrooms. Add 1 chopped garlic clove and cook for 4 minutes, until browned. Add 1 tsp butter, 1 tbsp cider vinegar and season.
Meanwhile, toast 4 slices of sourdough bread under the grill. Rub each piece with garlic, then top with a spoonful of mushrooms. Drizzle over a little fresh pesto, to serve.