Preheat the broiler.
Chop cauliflower into small florets.
1 head cauliflower
Heat a large pot of lighted salted water to boiling. Then parboil the cauliflower for 5 minutes. Drain.
Meanwhile, cut up the cheese into cubes and blitz in the food processor.
4 ounces cheddar cheese, 4 ounces gruyere, 1 ounce parmesan
Make the cheese sauce. In a small saucepan, melt the butter over medium-low heat, then add the flour, whisking constantly to make a roux.
2 tablespoons unsalted butter, 2 tablespoons flour
Slowly pour in the milk, whisking constantly,until the sauce is thickened (some say "until it coats the back of a wooden spoon").
2 cups milk
Remove from heat. Add in about ⅖ of the cheese (you'll need to reserve enough to top the cauliflower), the paprika, and salt and pepper to taste.
¼ teaspoon smoked paprika
When the cauliflower and cheese sauce are both done, mix them together into the pot and then add to a broiler safe baking dish. Top with the remaining cheese and slide under the broiler until just starting to brown.