25g freshly grated parmesan, plus a little extra for the top
A pinch of grated nutmeg, to taste
How to make
Melt the butter in a wide deep frying pan with the oil and add the mushrooms, garlic and sage and fry gently until soft for about 10 minutes. Sprinkle in the flour and stir well to mix, then pour in the stock, stirring constantly for 5 minutes as it thickens. Add the pinto beans and season well, turn off the heat and set aside.
Meanwhile, break the egg into a mixing bowl and lightly beat. Pour in the cream and beat together before stirring through the cheddar and the parmesan. Season to taste with salt and pepper and a little nutmeg.
Preheat the oven to 200°C / 180°C fan / gas 6. Take a large baking dish – about 22cm x 26cm – and pour in half the mushroom sauce. Lay on 4 sheets of lasagne, trying not to overlap them (snap off any overlapping bits if necessary). Pour in the remaining mushroom sauce and lay over the rest of the lasagne.
Finally pour on the cream and cheese sauce and add a final grating of parmesan. Bake in the oven for 30 minutes until golden and bubbling. Serve with a big green salad.