Melt the butter and sprinkle in the flour. Over a medium heat stir with a wooden spoon until you cook out your roux base. Add milk, cream, mustard and the seasoning and stir for 5 mins on a low heat until the sauce thickens.
Add grated cheese and stir until melted. Remove from the heat and add an egg yolk for extra gloss and richness. Finish the cheese sauce with minced truffle.
Preheat your oven to 180?C and blanche your cauliflower florets in boiling water. Arrange the caulk leaves around your ovenable dish and then place your blanched cauliflower florets into the middle. Pour over your cheese sauce and top with some finely grated parmesan.
Roast for 15 minutes until golden brown and the cheese is bubbling.
Finish with slices of black Truffle and serve hot.