MAKE CASSEROLE: Mash your pre-boiled/baked and peeled sweet potatoes in a large bowl. Once they're mashed to your liking, stir in the sugar, butter, vanilla extract, milk, eggs, and additional pecans, if including. Mix to combine. Transfer sweet potato mix into a 9x13 baking dish.
5 cups sweet potatoes (~5 medium potatoes),, 1 cup granulated sugar, 8 tbsp softened butter, 1 1/2 tsp vanilla extract, 1/2 cup milk, 2 large eggs, 1/4 cup chopped or halved pecans (optional)
MAKE CRUMBLE TOPPING: In a bowl, mix brown sugar, flour, pecans, and butter together and make sure it's well combined. Then spread it evenly across the top of your sweet potato mixture - do not mix it into the casserole, rather put a layer over the top.
1 cup brown sugar, 1/2 cup all-purpose flour, 4 tbsp softened butter, 1 cup chopped pecans