Sweet Potato Casserole with Graham Cracker Streusel

Preheat oven to 425ºF. 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 350ºF. 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.