2) Melt the butter in a small saucepan over low heat. With a wooden spoon, stir in the flour and cook, stirring constantly, for 2 minutes.
3) Off the heat, whisk in the hot milk, 1/2 tsp salt, 1/4 tsp black pepper, the cayenne and nutmeg. Cook over low heat, whisking constantly, for 1 minute, until smooth and thick.
4) Off the heat, while still hot, whisk in the egg yolks, one at a time. Stir in the Roquefort and the Parmesan and transfer to a large mixing bowl.
5) Put the egg whites, cream of tartar and a pinch of salt in the bowl of an electric mixer fitted with the whisk attachment. Beat on low speed for 1 minute, on medium speed for 1 minute, then finally on high speed until it forms firm, glossy peaks.
6) Whisk 1/4 of the egg whites into the cheese sauce to lighten and then fold in the rest. Pour into the souffle dish, then smooth the top. Draw a large circle on top with the spatula to help the souffle rise evenly, and place in the middle of the oven.
7) Turn the temperature down to 190C/Gas 5. Bake for 30 to 35 minutes (don't peek!) until puffed and brown. Serve immediately.