1: Fry 1 sausage. Sausages vary enormously in size, but this doesn't really matter. Fry about 100g of sausage and use what you like of it later in the recipe.
3: Prepare the marinade by mixing 3 tablespoons lemon juice, 3 tablespoons olive oil, 1 shallot, some finely chopped parsley, salt and pepper.
4: Drizzle the marinade over the mushrooms, mix well and leave in the fridge to marinate for at least 1 hour, covered with plastic film. This can be done the day before.
5: Chop the mushroom stalks into small pieces.
6: Pour 2 tablespoons olive oil into a small frying pan on high heat. When hot, add 1 shallot, chopped finely. Salt, pepper and cook for 1 minute without colouring.
7: Add the chopped mushroom stalks and sauté for 2 or 3 minutes. Salt after cooking and set aside.
8: Preheat the oven to 390°F (200°C). Sit the mushroom caps on a wire rack and stand this on a baking tray lined with a sheet of cooking parchment. Put the mushrooms in the oven for 20 minutes. This will not fully cook them, just make them release their water.
9: Meanwhile, cut the sausage into small pieces and grate the cheese, if not already done.
10: Use a fork to crush 100 g cooked potatoes in a bowl.
11: Add the sausage pieces, half the grated cheese, the sautéed mushroom stalks and any remaining marinade. Salt and pepper, then check the seasoning.
12: Take the mushrooms out of the oven and turn them over...
13: ...then fill with the stuffing mixture. Scatter the rest of the grated cheese over the top.
14: Return to the oven to brown for 10 to 15 minutes.
15: Serve either hot or warm.
Remarks
Choose large mushrooms if possible as thesy are easier to fill. Portobello or field mushrooms are ideal, but use whatever you prefer.