Preheat the oven to 400 degrees F (200 degrees C).
Prick the Sweet Potato (4 pound) several times with the tines of a fork, and bake for 1 hour, or until tender when tested with a knife. Set aside.
Meanwhile, heat Unsalted Butter (4 tablespoon) in a medium sauté pan. Cook the butter over medium-low heat for three minutes, watching carefully, until brown flecks begin to form.
Immediately remove the pan from the heat and add the Shallot (2 cup) and Brown Sugar (1 tablespoon). Cook over medium-low heat for 20 minutes, stirring occasionally, until the shallots are tender and lightly browned. Set aside.
In a medium bowl, combine the Walnut (1 1/2 cup), All-Purpose Flour (3/4 cup), Parmesan Cheese (1 cup), Fresh Sage (2 tablespoon), Crushed Red Pepper Flakes (1/4 teaspoon), Brown Sugar (2 tablespoon), the remaining Unsalted Butter (5 tablespoon), and Kosher Salt (to taste) (1 tsp).
Using your fingers, pinch the mixture together to form large crumbles. Set aside.
Peel the potatoes and place the flesh in a large mixing bowl, discarding the skin. With a hand mixer on low speed or a potato masher, beat the potato mixture until smooth.
Fold in the shallot mixture, the remaining Brown Sugar (1 tablespoon), Whole Milk (1/2 cup), remaining Crushed Red Pepper Flakes (1/4 teaspoon), and Kosher Salt (to taste) (around 2 tsp). Stir to combine.
Lower the oven temperature to 375 degrees F (190 degrees C).
Transfer to a 9x13-inch. Sprinkle the crumble mixture evenly over the potatoes and bake for 30 minutes, until the crumble is browned and the potatoes are heated through.
Serve hot and enjoy!