Keto Cauliflower Mac and Cheese

Preheat the oven to 425 degrees F (220 degrees C).

Place cauliflower in a large pot and cover with water and bring to a boil. Reduce heat to medium-low, cover, and simmer until fork-tender, about 5 minutes. Drain.

Meanwhile, combine Cheddar cheese, Colby-Monterey Jack cheese, sour cream, mayonnaise, and onion in a large bowl. Add drained cauliflower and mix until cauliflower is well coated with cheese mixture. Transfer to an oven-safe casserole dish. Sprinkle 1/2 cup Cheddar cheese on top.

Bake in the preheated oven until top is golden brown and cheese is completely melted, about 30 minutes.