Preheat the oven to 350°F and butter a 2-quart baking dish. Place Sweet Potatoes in a pot with an inch of cold water over the potatoes. Bring to a boil. cook for 7–10 minutes, until just barely tender, we don’t want these turning into mashed sweet potatoes. Drain thoroughly and let steam-dry for a few minutes.
Melt the butter in a light-colored saucepan over medium heat, swirling frequently, until the milk solids turn golden brown and smell nutty, about 4–6 minutes. Immediately reduce the heat to low and stir in the brown sugar, maple syrup, cinnamon, and salt. Simmer gently for 2–3 minutes, stirring until glossy and slightly thickened. Remove from the heat and stir in the vanilla.
Gently fold the sweet potato chunks into the glaze until each piece is generously coated. Transfer to the prepared baking dish, scraping all the glaze over the potatoes.
In a bowl, combine the chopped pecans, graham cracker crumbs, melted butter, brown sugar, and salt. Stir until evenly moistened and small clumps form.
Sprinkle the pecan-graham crumble evenly over the glazed sweet potatoes. Bake uncovered for 15–20 minutes, until the glaze is bubbling around the edges and the casserole is heated through.
Scatter the mini marshmallows evenly over the crumble. Bake for another 5–8 minutes, until puffed and softened. For a toasted finish, broil for 1–2 minutes, watching constantly, until golden brown.
Serve. Let the casserole rest for 5 minutes before serving. Spoon into bowls while the glaze is glossy and the marshmallow topping is warm and gooey.