Preheat oven to 400°FPlace sweet on a baking sheet lined with foil. Prick the top and sides with a fork and place in the oven—Bake for 45 minutes or until fork-tender.
Meanwhile, melt the butter in a heavy bottom saucepan on medium-low heat for 3-5 minutes or until slightly brown.
Peel the baked potato and place in a bowl. Use a ricer or potato masher and mash until you reach the desired consistency. Add the brown butter, cream, salt, pepper, nutmeg, cinnamon, and cardamom. Combine until thoroughly mixed.
Turn the oven down to 375°F.Spray a baking casserole dish with cooking spray. Add the sweet potato to the casserole, and top with pecans and marshmallows. Place in the oven and bake for 15 minutes or until the top is slightly brown. Remove from the oven and serve warm.
If you plan to make this recipe ahead of time, don’t add the pecans and marshmallows until you are ready to bake. It's best to let the casserole dish get to room temperature before placing it in the oven. You don't want to shatter the dish and ruin dinner ;)
If you intend to serve the dish later, don’t add the marshmallow until 15 minutes before serving time. The marshmallow will melt into a puddle if it’s left sitting out for a while.
Cut down cooking time by cooking the potatoes on a stovetop until fork-tender, then continue with the rest steps.