Steam the cauliflower by bringing a couple of inches of water to a boil in a stockpot. Put chopped cauliflower in a steamer basket and set in pot. Cover the pan and steam for 8-10 minutes until cauliflower is very soft.
Drain cauliflower and put on a paper towel lined plate. Let sit for 5-10 minutes and then squeeze all moisture out by blotting with additional paper towels (THIS IS VERY IMPORTANT - IF THE CAULIFLOWER IS TOO WET, YOUR MASH WILL BE SOUPY).
Mix cauliflower, pumpkin, heavy cream, cinnamon and brown sugar substitute in a blender until smooth.
Pour into a 9x9" baking pan and bake for 15 minutes.
While it's baking, add mascarpone to a microwave-safe bowl and microwave in 15-second intervals until melted. Mix in stevia and vanilla.
Remove pan from oven and drizzle with mascarpone mixture and then sprinkle with pecans. Serve immediately.
Nutrition Info Per Serving: Calories 200 Total Fat 17 g Cholesterol 48 mg Sodium 302 mg Potassium 411 mg Total Carbohydrate 11 g Dietary Fiber 4 g Sugars 5 g Protein 4 g