The night before your meal, clean, peel, and chunk the sweet potatoes. I like to leave mine in bigger-than-bite-sized chunks. Place the cut up potatoes in a large baking dish. Use a dish big enough that the potatoes are mostly in a single layer.
Combine butter, brown sugar, and orange juice in a mixing bowl. Pour sugar mixture over potatoes. Sprinkle with pumpkin pie spice and top with a handful of miniature marshmallows, which will melt into the sauce.
Cover with plastic wrap and microwave for 20 minutes, or until the potatoes are fork tender. If you're making ahead, allow the potatoes to cool and refrigerate until it's time to serve. If not, just move on to the next step.
To serve: Top with remaining marshmallows and bake at 375 for 10 minutes (20 minutes if chilled), until the potatoes are hot and marshmallow topping is just toasted.