Preheat your oven to 400°F (200°C). Peel and chop the sweet potatoes into equal-sized chunks, then toss them in a mixing bowl with olive oil, cinnamon, and nutmeg until evenly coated. Spread the sweet potatoes out on a baking sheet and roast for 50-60 minutes, or until they are fork-tender and lightly caramelized.

Once the sweet potatoes are roasted, reduce the oven temperature to 375°F (190°C). In a large mixing bowl, combine the soft sweet potatoes with almond milk, vanilla extract, brown sugar, maple syrup, and allspice. Stir in the raisins until well blended and creamy.

Grease a 9x13-inch baking dish with olive oil or vegan butter. Spoon the sweet potato filling into the dish, smoothing the top with a spatula. Dot with small pieces of unsalted butter or vegan butter and press in some extra marshmallows.

In a separate bowl, mix raw pecans with a splash of maple syrup until well coated. Sprinkle the pecan mixture evenly over the sweet potato filling. Cover the dish with aluminum foil.

Place the casserole in the preheated oven and bake for 15 minutes. Remove the foil and continue baking for another 15 minutes, or until the top is golden and the marshmallows have melted.

After baking, let the Maple Sweet Potato Casserole cool for about 10 minutes before serving. This allows the casserole to set up slightly.