The Ultimate Creamy Threecheese Cauliflower Gratin

Prepare and Blanch the Cauliflower: Core the cauliflower and cut it into medium, uniform florets (about 3 cm/1.5 inches). Bring a large saucepan of salted water to a rolling boil. Add the florets and cook for exactly 3 to 4 minutes (al dente). Immediately drain the cauliflower and spread it on a clean tea towel to dry thoroughly. Place the dried florets into a 9x13 inch ovenproof baking dish.

Build the Béchamel Base (Roux): In a medium saucepan, melt the 50g of butter over medium heat. Whisk in the flour until a smooth paste (the roux) forms. Cook for 1 to 2 minutes, stirring continuously, until the mixture smells nutty but has not browned.

Thicken the Sauce: Remove the pan from the heat. Gradually pour in the cold whole milk, whisking vigorously the entire time to prevent lumps. Return the pan to medium heat. Bring the sauce to a gentle simmer, stirring constantly, and cook for 5 to 7 minutes until the sauce is thick enough to coat the back of a spoon.

Create the Mornay Sauce: Remove the thickened Béchamel from the heat. Stir in the salt, pepper, nutmeg, and Dijon mustard. Add 100g of the grated Sharp Cheddar and the 50g of Gruyère or Swiss cheese. Stir until the cheese is completely melted and the sauce is smooth and velvety. Pour the warm Mornay sauce evenly over the prepared cauliflower in the baking dish.

Prepare and Sprinkle the Topping: Preheat the oven to 200°C (400°F). In a small bowl, combine the Panko breadcrumbs, the reserved 50g of Cheddar cheese, and the olive oil or melted butter. Toss well until coated. Scatter the crispy topping evenly over the sauce.

Bake and Rest: Bake for 30 to 35 minutes, or until the sauce is bubbling around the edges and the topping is deeply golden brown and crisp. Remove the gratin from the oven. Let it rest for 10 minutes before serving to allow the sauce to set slightly.