Preheat oven to 200°C/400F/Gas Mark 6.

Bring a large saucepan of salted water to the boil. Add the brussels sprouts and blanch for 3 -4 minutes or until bright green and tender. Lift the broccoli from the water into a colander. Then, add the cauliflouwer florets, and continue simmering for 5-6 minutes until soften. Drain and transfer both to the prepared gratin dish.

Meanwhile, melt some butter in a saucepan over a medium heat and stir in the flour. Cook for about 2 minutes until a light golden colour. Pour in the milk and whisk vigorously until smooth.

Bring the sauce to a simmer and cook for 5 -6 minutes. Remove from the heat and add the cheese, stirring until melted.

Pour the sauce over the vegetables and season with salt and black pepper. Place the dish in the oven and bake for 10 -15 minutes until golden.

Serve immediately.