TO ROAST THE SWEET POTATOES:
Begin by preheating the oven to 400 degrees Fahrenheit and prepare a baking sheet by lining it with parchment paper.
In a bowl, add the cubed sweet potatoes along with the olive oil, cinnamon, and nutmeg, gently mixing everything together until sweet potatoes are fully coated.
Add the sweet potatoes unto the baking sheet (in a single layer) and and bake for 50-60 minutes or until sweet potatoes are tender, charred, and golden. Remove from oven and let cool slightly.
TO MAKE THE CASSEROLE FILLING:
Preheat the oven to 375 degrees Fahrenheit and lightly grease a large 9x13 baking dish.
In a bowl, add the roasted sweet potatoes, milk, vanilla, brown sugar, maple syrup, cinnamon, nutmeg, allspice, raisins, and marshmallows, mixing everything together until combined. NOTE: It's OK if some of the sweet potato starts to mash. You want a mixture of mashed + chunks.
Scoop the mixture into prepared baking dish, evenly spreading everything out. Add the pieces of butter in between parts of the casserole mixture. For a little extra goodness-----tuck in a few additional marshmallows into the sweet potato mixture, pressing them in gently all around.
TO MAKE THE TOPPING:
In a bowl, add the pecans and maple syrup, stirring until combined.
Generously add the topping over the sweet potato casserole mixture until fully covered. Cover with foil paper.
Bake the casserole with foil for approximately 15 minutes in the preheated oven and then remove foil and finish baking for the remaining 15 minutes or until top is golden brown and the marshmallows have melted.
Remove the casserole from the oven and let it cool slightly before serving with your favorite sides and main dish.
Bon Appetit!