Sweet Potato Casserole With Graham Cracker Streusel

["Preheat oven to 425u00b0F. Arrange potatoes on a foil-lined rimmed baking sheet, then prick all over with a fork. Bake until the tip of a paring knife inserts easily into center of largest potato, 50-65 minutes, depending on size of potatoes. Let sit until cool enough to handle.", "Reduce oven temperature to 350u00b0F. Remove and discard potato skins. Transfer flesh to a large bowl and let cool completely. (You should have 4-4 1/2 cups.)", "Place graham crackers in a resealable plastic bag. Coarsely crush with your hands into 1/2""-1"" pieces. Transfer graham crackers to a medium bowl. Add pecans and 1/4 tsp. salt. Mix in 4 Tbsp. butter to combine.", "Add milk, maple syrup, cocoa powder, vanilla, pepper, and remaining 2 Tbsp. butter and 1 1/2 tsp. salt to bowl with potato. Mash with a potato masher or fork until smooth.", "Transfer potato mixture to skillet or baking dish. Sprinkle graham cracker mixture over. Bake casserole until streusel is lightly golden, 20-25 minutes. Sprinkle marshmallows over, then continue to bake until marshmallows are lightly golden, 10-15 minutes more. Let sit 10-15 minutes. Serve warm.", "Potatoes can be baked and peeled 5 days ahead. Transfer to an airtight container and chill. Potato filling can be made 3 days ahead. Transfer to an airtight container and chill. Bring to room temperature before using."]