Cook the cauliflower for about 3-5 minutes or al dente either by boiling in a large pot of water or vapour. Drain well, for approximately 10 minutes.
While cauliflower is draining, in a medium / large pot add the butter and melt, then whisk in the flour, salt, pepper and thyme.
Then slowly add the milk, stirring constantly, bring to a boil and boil for approximately 2-3 minutes until thickened.
Place 2-3 tablespoons of white sauce on the bottom of the 8 inch baking dish. Add the drained cauliflower and cover with remaining white sauce. Then sprinkle with the parmesan cheese. Bake for 15 minutes, then raise the heat to 400F (200C) and bake for another 5 minutes or until golden. Let sit 5 minutes then serve. Enjoy!