Preheat your oven to 400°F (200°C). Toss the peeled and cubed sweet potatoes in a large bowl with olive oil, cinnamon, and nutmeg until evenly coated. Spread them out in a single layer on a parchment-lined baking sheet, then roast for 50-60 minutes, or until they're tender and slightly caramelized.

Once the sweet potatoes are done roasting, reduce the oven temperature to 375°F (190°C). In a mixing bowl, mash the roasted sweet potatoes lightly, leaving some chunks for texture. Add in almond milk, vanilla extract, brown sugar, maple syrup, ground spices, soaked raisins, and marshmallows. Mix well until combined, creating a creamy filling with delightful sweetness.

Pour the sweet potato mixture into a greased 9x13 inch baking dish, smoothing it out evenly. Sprinkle the cubed butter over the top. If desired, tuck in some extra marshmallows into the filling for a gooey surprise.

In a small bowl, combine the raw pecans with maple syrup, ensuring each piece is well coated. Sprinkle this pecan mixture generously over your assembled casserole.

Cover the casserole with foil and bake in the preheated oven for 15 minutes. Afterward, carefully remove the foil and bake uncovered for an additional 15 minutes until the topping is golden brown and the marshmallows are melted.