Warm the egg whites in a large bowl to room temperature (about 1 hour), and preheat the oven to 200°C.
Butter a 1.5-liter soufflé dish and sprinkle the bottom and sides with Parmesan.
Melt the butter in a pot, work in the flour, and whisk until smooth and bubbling.
Remove from the heat, pour in the milk, stir until smooth, then work in the salt, mustard powder, cayenne and Worcestershire sauce.
Return to the heat and cook until thick for 1 minute, then remove and work in the egg yolks one at a time.
Pour into a large bowl, and work in most of the cheese (set aside one tablespoon) and the chopped chili.
Beat the egg whites with a pinch of salt until stiff, stir in one portion into the egg base, then gently fold in the rest.
Pour into the soufflé dish, sprinkle with the reserved cheese on top, and run the tip of a sharp knife in a circle about 2.5 cm from the edge (this makes the top rise evenly).
Bake in the oven, turned down to 180°C, for 35-40 minutes, until risen and a knife inserted comes out clean. Serve immediately.