📖 Instructions

1. **Step 1: Prep the Sweet Potatoes for Boiling.** Start by washing your sweet potatoes thoroughly under cold running water. It's important to get rid of any dirt. Then, with a sturdy vegetable peeler, carefully remove the skin from each sweet potato. Once peeled, place them on a cutting board and cut them into roughly 1-inch to 1.5-inch cubes. Try to make the cubes similar in size; this ensures they cook evenly and become tender at the same time.
2. **Step 2: Boil Until Fork-Tender.** Place the cubed sweet potatoes into a large pot. Fill the pot with cold water, making sure the water covers the potatoes by about an inch. Add a generous pinch of salt to the water; this helps season the potatoes from the inside out. Bring the water to a rolling boil over medium-high heat. Once boiling, reduce the heat slightly to maintain a gentle simmer and cook for 15-20 minutes, or until the sweet potatoes are incredibly fork-tender. You should be able to easily pierce them with a fork without much resistance. Don't overcook them to the point of mush, but make sure they're soft enough to mash smoothly.
3. **Step 3: Drain and Mash.** Carefully drain the cooked sweet potatoes using a colander. Make sure to drain them really well; any excess water will make your casserole watery. Transfer the hot, drained sweet potatoes to a large mixing bowl. Now, grab a potato masher, a large fork, or even a ricer if you have one. Begin to mash the sweet potatoes until they are smooth and free of lumps. You want a creamy, consistent texture here. A few small lumps are okay if you prefer a slightly chunkier casserole, but generally, smooth is the way to go for this dish.
4. **Step 4: Incorporate the Flavorful Fats and Spices.** To the mashed sweet potatoes, add the unsalted butter (make sure it's softened or melted for easier mixing), light brown sugar, granulated sugar, whole milk or heavy cream, vanilla extract, ground cinnamon, and ground nutmeg. These ingredients are key for that signature rich, sweet, and spiced flavor. Mix everything together really well. You can use a wooden spoon or an electric hand mixer on low speed. Continue mixing until all the ingredients are fully combined and the mixture is smooth and creamy. Taste a small bit and adjust seasonings if needed—maybe a tiny bit more cinnamon or a pinch of salt to balance the sweetness.
5. **Step 5: Prepare for Baking.** Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with butter or cooking spray. This prevents the casserole from sticking and makes cleanup a breeze. Carefully spoon the sweet potato mixture into the prepared baking dish. Spread it out evenly with the back of your spoon or a spatula, creating a smooth, level surface. This helps ensure even baking and a nice base for your marshmallows.
6. **Step 6: Add the Marshmallow Topping.** Arrange the mini marshmallows evenly over the top of the sweet potato mixture. Don't be shy here! You want a nice, generous layer. If you're using larger marshmallows, you might want to cut them in half so they cover the surface better and toast more evenly. Try to get them in a single layer or a slightly overlapping layer for the best golden crust. Avoid piling them too high, or the ones underneath won't toast as well.
7. **Step 7: Bake to Golden Perfection.** Place the baking dish into your preheated oven. Bake for 25-30 minutes. During the first 20-25 minutes, the sweet potato mixture will heat through and firm up slightly. For the last 5-10 minutes, keep a close eye on the marshmallows! They will puff up and turn a beautiful golden brown. If they're browning too quickly, you can loosely tent the dish with aluminum foil. If you want an even darker, slightly crispier marshmallow topping, you can switch your oven to broiler mode for the last 1-2 minutes, but watch it like a hawk—marshmallows can go from golden to burnt in seconds under the broiler!
8. **Step 8: Cool and Serve.** Once the marshmallows are perfectly toasted to your liking, carefully remove the casserole from the oven. Let it rest for about 5-10 minutes before serving. This allows the casserole to set slightly and the marshmallows to cool just enough so they're not scalding hot, but still wonderfully gooey. Serve warm and watch it disappear!