Preheat the oven to 220 degrees.

Chop the cauliflower into florets and add to a pan of salted, boiling water. Cook for approximately 10 minutes until soft, then drain and leave to one side.

Put a frying pan on a medium heat. Add the pancetta and sizzle until starting to crisp, then add the chopped onion and halved mushrooms. Cook for around 5 minutes, then take off the heat.

In another saucepan, melt the butter over a medium heat then stir in the flour. Cook for 2 minutes, then remove from the heat and gradually whisk in all of the milk. Put back on the heat and cook, whisking all the time, until it thickens. Remove from the heat again, stir in the grated cheddar and season with salt and pepper.

Take an oven proof dish and pile in the cauliflower. Drain any liquid from the pancetta and mushroom mix, then add the mixture to the dish. Pour over the cheese sauce, sprinkle over the parmesan and bake in the oven for 20 minutes until golden.