Boil cauliflower and onion in enough salted water to cover, until they are just tender. (10 - 15 minutes) Be careful not to overcook. Drain well.
Arrange the cauliflower and onion in a shallow ovenproof dish, and scatter over the chopped egg.
Put the flour, curry powder and butter/margarine in a saucepan, and cook gently, stirring constantly, to a smooth paste. Add the milk gradually, stirring all the time, gradually bring to the boil, stirring well, until thickened and smooth.
Stir in the thyme and seasoning and allow the sauce to simmer for a minute or two.
Remove from the heat, and stir in about 3/4 of the cheese.
Pour the sauce over the cauliflower, scatter over the croutons, and sprinkle with the remaining cheese.
Brown under a hot grill until golden and serve. Delicious with thick crusty bread.