Combine the cauliflower, butter, salt, pepper, and garlic powder in a microwave safe bowl.Microwave on high for six minutes - or until the cauliflower is tender and done to your liking.Add the mascarpone cheese and microwave on high for 2 more minutes.Add the parmesan cheese and stir until fully blended and creamy. Cool for 2 minutes (so you don't cook the pesto when you add it and lose the green color.)Stir in the basil pesto and serve warm.