Preheat oven to 425°F. Toss the cauliflower florets with 2 tablespoons of olive oil and a couple pinches of salt and pepper. Spread the florets evenly on a baking sheet.

Cut just the top off the head of garlic (enough to expose the cloves), drizzle 1 teaspoon of olive oil over the top, and then wrap the garlic in tin foil. Place it on the sheet pan with the cauliflower.

Roast the garlic and cauliflower for about 30 minutes, just until the cauliflower is tender and nicely browned in places.

While the cauliflower is roasting, prepare the bechamel sauce. First, heat the milk in a saucepan until it just starts to simmer.

While the milk is heating, in another saucepan melt the butter over low heat until frothy. Sprinkle in the flour and stir until it forms a paste.

Slowly pour in the hot milk, whisking continuously to ensure no lumps form and the roux fully incorporates into the milk. Raise the heat to bring the pot to a simmer.

Place the onion wedge in the milk mixture. Let the mixture simmer and thicken for about 20 minutes or so, or until it has reduced enough to coat the back of a spoon. You will need to stir frequently to ensure the bechamel does not burn on the bottom of the pan. Once thickened remove the onion. If your sauce has lumps you can strain it, but this is optional.

Squeeze out the cloves and mash them with a fork. Add the garlic to the sauce and stir to combine.

Stir in 1 1/2 cups of the grated cheese until it's melted into the sauce. At this point taste for seasoning and add in some salt and pepper (I added 1/2 teaspoon of salt and 1/4 teaspoon of pepper, but season to your taste).

Gently fold the roasted cauliflower florets into the sauce. Pour the mixture into an 8 x 8 baking dish, top with the remaining cheese. Place it under the broiler until the cheese melts and starts to brown a bit on top. Remove from the oven and serve.