Preheat the oven to 400 and lightly grease a good-sized casserole.  Drop the cauliflower into a large pot of boiling water for 5 minutes, and drain thoroughly.

In a medium pot (I used my non-stick skillet), heat the oil over medium heat and saute the onion and garlic for a few minutes until it’s just starting to soften.  Whisk in the flour and keep whisking until the flour is integrated – it will be lumpy – then carefully pour in the hot milk and continue to whisk until the mixture comes to a boil.  Boil for about a minute, while whisking, until it thickens.

Remove the pot or skillet from the heat and stir in the grated cheeses, salt, pepper and nutmeg, then pour about a third of the sauce across the bottom of your prepared casserole.  Evenly add all of the well-drained cauliflower, and then cover it over with the rest of the sauce.  If I was serving this to company, I’d definitely combine the ‘topping’ ingredients and sprinkle them on (and it would have made for a better picture), but it was super tasty as is.  Bake at 400 for about 20 minutes until it’s bubbling and the top has just started to brown.