Preheat the oven to 350 degrees F. Arrange an oven rack in the middle of the oven.
Butter or spray with baking spray a 9x13-inch casserole or baking dish. Set aside.
Add 1 cup of pecans to a baking sheet and roast for a few minutes. Watch closely to not burn them. Remove from oven, cool, and roughly chop.
Cook Sweet Potatoes:
In the meantime, add the cubed potatoes to a dutch oven or large saucepan. Cover with water and sprinkle some salt, bring to a boil. Boil for about 15 minutes, when pierced with a fork, the potatoes should be tender.
Drain cooked sweet potatoes, mash until very smooth, and set aside to cool off a bit.
Combine the sugar and cinnamon in a small bowl. Stir and set aside.
In a medium bowl combine: melted butter, brown sugar, beaten eggs, cream, vanilla, salt, and flour. Whisk well to combine, a hand mixer can be used as well.
Add the mixture to the mashed sweet potatoes and stir until well combined. A hand mixer can be used for this as well.
Transfer the mixture to the prepared baking dish. Smooth the top.
Sprinkle with chopped pecans and cinnamon sugar evenly. Drizzle the remaining 3 tablespoons of melted butter on top.
Cover the dish with foil, to avoid the pecan topping from burning. Bake for about 30 minutes, uncover and bake for another 20-30 minutes or until puffed and lightly browned on the edges and top.
Serve immediately or cool and refrigerate for later.