Preheat oven to 400 degrees F.

Bring a large pot of water to boil and cook cauliflower until just barely tender, about four minutes. Drain thoroughly and place into a medium-sized casserole.

Melt butter in a medium-sized saucepan over medium-high heat. Add flour and whisk a minute or two until flour starts to look a little dry but hasn’t picked up any color. Whisk in milk, bring to a boil and stir until thickened enough to coat the back of a spoon and not fill in the line when a finger is run across it.

Remove from heat and add cheese, in small handfuls, stirring after each until incorporated. Add most of the thyme, salt, and pepper.

Pour the sauce over the cauliflower, using a spoon to nudge between florets, if necessary, so all are coated. If desired, top with a little additional cheese and sprinkle the top with a pinch of the thyme.

Bake for 20 minutes or until lightly browned in spots.