Spray the inside of an 8-quart slow cooker with non-stick spray. Place the peeled and diced sweet potatoes into the slow cooker. This step gets everything ready for combining the remaining ingredients.

Add the brown sugar, maple syrup, butter pieces, pumpkin pie spice blend, and salt to the diced sweet potatoes in the slow cooker. Stir well to thoroughly combine all the ingredients. This ensures every sweet potato piece gets coated in the flavorful mixture. I like to use a big spoon or spatula to make sure nothing sticks and all the pieces are evenly coated.

Cover the slow cooker with its lid and set it to cook on high for 4 hours, or until the sweet potatoes are fork tender. There may be extra sauce at the bottom when cooking is complete—you can pour it off if you want, or leave it in to drizzle over the finished sweet potatoes.

About five minutes before serving, remove the lid and scatter the miniature marshmallows on top of the cooked sweet potatoes. Replace the lid and allow the marshmallows to melt for 3 to 5 minutes. Serve immediately! For an even gooier topping, I sometimes let the marshmallows sit a minute longer—the extra melt makes it special.