Toss the cauliflower and garlic with the olive oil and spread out on a baking sheet. Roast for 20 minutes, or until the cauliflower is tender and golden brown.
Meanwhile, melt the butter in a medium saucepan over medium-low heat. Add the flour and whisk until lightly golden, about 1 minute. Slowly whisk in the milk and cook, stirring constantly, until the sauce thickens, about 5 minutes.
Remove the sauce from the heat and stir in the salt, pepper, and cheese. Add the roasted cauliflower and garlic and mix to combine.
Pour the cauliflower mixture into a greased baking dish and top with the breadcrumbs. Bake for 25 minutes, or until the top is golden brown and bubbly.
Interesting Facts
Cauliflower is a member of the cruciferous vegetable family.
Garlic is a natural antibiotic and anti-inflammatory.
Au gratin is a French term that means "with cheese and/or breadcrumbs".