Preheat oven to 350F. Peel and boil sweet potatoes in a covered saucepan until tender about 20 min. Drain and mash. Mix in the softened butter, sugar, vanilla, and milk. Pour into a baking dish or casserole. Bring cream to simmer in a small saucepan. Add brown sugar and stir until dissolved. Cook over medium heat to soft ball stage 235F. Remove from heat and beat in butter and pecans. Pour over sweet potato mixture. All of the above may be done up to 2 days in advance and stored in the fridge. Then just heat in the oven until bubbling hot and enjoy.