Combine the cauliflower, broccoli, butter, salt, pepper, garlic powder, and nutmeg in a medium sized microwave safe bowl and microwave on high for 4 minutes.
Stir.Microwave for an additional 2 minutes.
Stir.Add the cheddar cheese and microwave an additional 2 minutes.Remove from the microwave carefully and stir in the mascarpone cheese until creamy and fully incorporated.Taste and adjust seasoning as desired.Serve hot.