Preheat oven to 425°F and line a baking sheet with parchment paper.
Toss cauliflower florets with olive oil, salt, and pepper, then spread in a single layer on the baking sheet. Roast for 20 minutes until tender and lightly golden.
While cauliflower roasts, combine cream cheese, heavy cream, and garlic powder in a large saucepan over medium heat, stirring until smooth and creamy.
Add 1.5 cups of the shredded cheddar to the cream mixture and stir until melted and well combined.
Add roasted cauliflower to the cheese sauce and stir gently to coat. Transfer to a 9x13 inch baking dish.
Top with remaining cheddar cheese and broil for 2-3 minutes until bubbly and golden brown on top.