Preheat the oven to 350 degrees F.
In a large saucepan, bring 8 cups of water to a boil. While water is heating up, peel and chop the sweet potatoes into 1/2" inch cubes. Place in boiling water and boil for about 10 minutes until potatoes can be easily pierced with a fork.
Drain the water from the cooked sweet potatoes and let cool 10 minutes. Mash potatoes with a masher or large fork. Add the remaining sweet potato ingredients and blend together with an immersion blender or a wooden spoon. Transfer to a 2-quart casserole dish and spread evenly. To make the pecan topping, place pecans, flour, sugar, cinnamon, and salt in a food processor and pulse a few times to combine. Once pecans have broken into uniform pieces, add the melted butter while the motor still running. Pulse a few more times until the crust is fully hydrated. The pecan topping should stick together when pressed between your fingers. If it is too dry, add one additional tablespoon of melted butter.
Spread the pecan topping evenly over the sweet potato puree and bake for 20-30 minutes until topping is golden brown. Remove from heat and let cool 10 minutes before serving.