Preheat the oven to 375°F (190°C) and put a baking tray in the oven to heat. Lightly grease a large soufflé dish (about 1.75 litres) with the butter. Mix together the Parmesan and breadcrumbs and sprinkle half of this mixture over the bottom and side of the dish, turning the dish to coat evenly. Set aside.
Cut the cauliflower into small florets and cook in a steamer over boiling water for 8-10 minutes until very tender. Tip onto a plate and leave to cool for a few minutes, then purée with 100 ml of the milk in a food processor or blender to a smooth consistency.
Mix the cornstarch with a little of the remaining milk to make a smooth paste. Heat the rest of the milk until almost boiling, then pour onto the cornstarch mixture, stirring constantly. Return to the pan, add the bay leaf and stir over a medium heat until the sauce is thickened and smooth.
Pour the sauce into a large bowl and remove the bay leaf. Beat in the egg yolks, one at a time. Add the Stilton and stir until melted, then stir in the cauliflower purée, mustard and chives. Season to taste.
Whisk the egg whites in a large, clean bowl, until stiff peaks form. Whisk one-third of the whites into the sauce mixture to lighten it, then gently fold in the rest of the whites.
Spoon the mixture into the prepared soufflé dish and sprinkle the top with the remaining breadcrumb mixture. Set the dish on the hot baking tray and bake for 35 minutes or until well risen and golden brown. Serve at once.
Each serving: 18 g protein, 15.5 g fat of which 8 g saturates, 16 g carbohydrate, 2 grams fibre, 278 Calories