Heat the oven to 190°C/gas 5. Butter a 1.75-litre soufflé dish. Melt the butter in a small saucepan, remove from the heat and add the flour. Mix to a smooth paste. Slowly add a little milk and stir until blended. Repeat until all the milk has been added, then return to the heat, stirring constantly until the sauce thickens. Remove from the heat. Add the Roquefort, nutmeg and egg yolks, and mix. Whisk the egg whites until stiff. Fold in the Roquefort mixture until evenly blended. Pour into the soufflé dish and cook in the centre of the hot oven for 35-40 minutes until risen and golden. Serve at once.