Step 1: Preheat your oven to 375°F (190°C). Grease a 9×13 inch baking dish with butter or non-stick spray.
Step 2: Place the peeled and chopped sweet potatoes in a large pot. Cover with cold water and bring to a boil. Cook for 15-20 minutes, or until the sweet potatoes are fork-tender. Drain thoroughly.
Step 3: Transfer the drained sweet potatoes to a large mixing bowl. Add the melted butter, brown sugar, milk (or cream), cinnamon, nutmeg, ginger (if using), vanilla extract, and salt.
Step 4: Mash the sweet potatoes with a potato masher until smooth. Alternatively, use an electric mixer for an extra creamy consistency. Taste and adjust seasonings if necessary.
Step 5: Spread the mashed sweet potato mixture evenly into the prepared baking dish.
Step 6: Bake for 20 minutes, or until the sweet potato mixture is heated through and slightly bubbly around the edges.
Step 7: Remove the casserole from the oven. Evenly spread the mini marshmallows over the top of the sweet potato mixture.
Step 8: Return the casserole to the oven and bake for an additional 5-10 minutes, or until the marshmallows are golden brown and puffed. If you want a more deeply browned top, you can briefly place it under the broiler for 1-2 minutes, watching it very closely to prevent burning.
Step 9: Remove from oven and let stand for a few minutes before serving. Enjoy your delightful sweet potato marshmallow casserole dream recipe!