Preheat the oven to 220C/425F/Gas 7.
Mix together the mustard, cream, cheese and egg yolks into a bowl and season with salt and freshly ground black pepper. Add the broccoli and mix well.
Place the egg whites into a bowl and whisk until stiff peaks are formed when the whisk is removed.
Fold through the egg whites and cayenne pepper.
Heat the butter in a small ovenproof blini pan and add the soufflé mixture. Place into the oven to bake for 5-10 minutes, or until puffed up and golden.