Preheat oven to 375 degrees. Peel sweet potatoes and cut into a large dice. Place in a large saucepan and cover with cold water. Bring to a boil, then reduce to simmer for about 10 minutes until sweet potatoes are fork tender. Drain and return to pot.
Use a potato masher, ricer, or hand mixer to mash sweet potatoes to desired consistency. Add in remaining ingredients, through salt, and mix well. Pour mixture into a 9 x 9 inch baking dish or casserole dish.
Crumble Topping. To make the topping, toss together the brown sugar, pecans, and flour. Add in the diced butter and use your hands to incorporate. Sprinkle the topping over the sweet potatoes.
Bake, uncovered, for 30-35 minutes until bubbly and heated though. If the topping starts to get to dark during cooking, cover with foil or a lid.
You can make this entire dish ahead up to two days in advance and just bake before serving.