Step 1

Preheat the oven to 400ºF.

Step 2

Place 1 inch of water in a large pot with 1 teaspoon salt and bring to a boil. Add the cauliflower and cook until tender crisp, 6 to 7 minutes. Drain and set aside in a large bowl.

Step 3

Heat butter and oil in a large saucepan over medium heat. Add onions and cook about 2 minutes.

Step 4

Stir in flour. Reduce heat to low and cook, stirring continually 3 - 4 minutes, to cook out the flour.

Step 5

Add the milk and continue whisking, raising heat to medium-high until it comes to a boil and becomes smooth and thick, about 2 minutes stirring; season with 1/2 teaspoon salt and black pepper.

Step 6

Once it becomes thick, remove from heat completely onto another burner if possible. Add the cheddar cheese, 1/4 cup at a time mixing well until cheese is all melted.

Step 7

Stir in cooked cauliflower, then pour into a baking dish and bake until bubbly and golden, about 15 to 20 minutes. Then broil 2 minutes, or until the top is slightly browned.