- Preheat the oven to 210°C (Gas 7).
- Cut the peeled potatoes into slices and place in a pan of water. Bring to the boil then cook them for 5 minutes. Drain.
- In the meantime, wash and cut the broccoli florets and cook them in a pan of salted water for about 5 minutes once the water has come to the boil.
- Thinly slice the onions. Clean and slice the mushrooms.
- Fry the onions with a knob of butter. Add the mushrooms.
- Pour in the cream and add the crushed garlic.
- Stir the mushroom preparation and adjust the seasoning.
- Cut the cheese into pieces.
- Arrange the potatoes and broccoli in a baking dish, pour the sauce over them and arrange the cheese pieces.
- Bake in the oven for about 15-20 minutes to obtain a nice grilled crust. Serve immediately.
Tip: For a softer-flavoured gratin, replace the blue cheese with Cheddar cheese.