1. Preheat oven to 375. Grease a 2 quart square baking dish; set aside. In a dutch oven, cook cauliflower in boiling lightly salted water about 5 minutes or just until tender; drain. Transfer to a bowl of ice water to stop cooking. Drain again; set aside.
2. In a medium saucepan, melt butter over medium-low heat. Stir in flour. Cook and stir for 1 minute. Stir in half-and-half and the 1/2 cup milk. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 1 minute more. Remove from heat. Stir in Fontina cheese, the 1 T fresh thyme, the salt, the pepper.
3. Spread about 1 cup of the sauce evenly in the bottom of the prepared dish. Arrange cauliflower florets in an even layer in the baking dish. Spread the remaining sauce over the cauliflower.
4. Sprinkle gratin evenly with bread crumbs; drizzle evenly with olive oil. Bake for 25-30 minutes or until lightly browned and bubbly. If desired, sprinkle with additional snipped fresh thyme.
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