Preheat the oven to 425 degrees.

Butter an 8×8-inch baking pan and set it aside.

In a large bowl, toss the cauliflower with 2 tablespoons olive oil, ½ teaspoon salt. And ½ teaspoon pepper until well coated.

Arrange the cauliflower on a rimmed baking sheet.

Cut about ¼-½-inch off of the top of the head of garlic.  

Drizzle the remaining 1 tablespoon olive oil over the top and wrap the garlic in foil.

Place the packet on the baking sheet with the cauliflower.

Roast the vegetables in the oven for 30 minutes or until the cauliflower is tender and lightly browned.

When the cauliflower is tender and the garlic is roasted, remove the pan from the oven and set aside to cool.  

Meanwhile, make the sauce.

In a saucepan over medium heat, melt the butter until foamy.

Add the onion and saute until translucent – about 5 minutes.

Whisk in the flour and stir until it forms a paste.

Slowly whisk in the milk and heavy cream, whisking continuously to incorporate the milk into the roux.

When the mixture is smooth, increase the heat to medium-high and allow the mixture to simmer, stirring constantly until thickened and silky smooth – about 20 minutes.

Remove the head of roasted garlic from the foil and squeeze the garlic cloves into a small bowl.

Mash them with a fork and add to the bechamel sauce.  Stir to combine.

Stir in 1 ½ cups of cheddar cheese, the parmesan cheese, remaining ½ teaspoon of both salt and pepper, and hot sauce, and whisk until melted and the mixture is smooth.  Remove from the heat.

Add the cauliflower to a large bowl.

Pour the sauce over the cauliflower and toss gently to combine.

Spoon the cauliflower and sauce into the prepared pan and sprinkle the remaining ½ cup of shredded cheese on top.

Preheat the oven to 350 degrees.

Bake the cauliflower until bubbling and golden on the top – about 30 minutes.

Allow to rest for 5 minutes and sprinkle with parsley before serving.