📖 Instructions

1. Prep the Sweet Potatoes: First things first, grab your sweet potatoes. Give 'em a good scrub under cold running water. You don't need to peel them just yet, as boiling with the skins on helps retain more nutrients and flavor, and makes peeling a breeze later. Cut the larger potatoes into roughly equal-sized chunks, say 2-inch pieces. This ensures they cook evenly.
2. Boil 'em Until Tender: Place the sweet potato chunks into a large saucepan or pot. Cover them with cold water by about an inch. Add a pinch of salt to the water – this seasons the potatoes from the inside out. Bring the water to a rolling boil over medium-high heat. Once boiling, reduce the heat to medium-low, cover, and let them simmer gently for about 15-20 minutes. You're looking for fork-tender here; a fork should slide into a potato piece with absolutely no resistance.
3. Drain and Dry: This step is crucial for a non-watery casserole! Once tender, drain the sweet potatoes thoroughly in a colander. Let them sit there for about 5 minutes, allowing as much steam as possible to escape and excess water to evaporate. You can even give the colander a gentle shake or two. Don't skip this.
4. Peel and Mash: Now that they've cooled a bit, the skins should slip right off. Peel them carefully (they’ll still be warm!). Transfer the peeled, cooked sweet potatoes to your large mixing bowl. Grab your potato masher or, for extra creaminess, an electric mixer. Mash the potatoes until they are smooth, with no lumps remaining. If using an electric mixer, start on low speed and gradually increase.
5. Mix in the Good Stuff (The Filling): To the mashed sweet potatoes, add the softened unsalted butter, granulated sugar, light brown sugar, whole milk (or heavy cream for an even richer result), vanilla extract, ground cinnamon, and ground nutmeg. Using your rubber spatula or electric mixer (again, low speed), mix everything together until it's completely combined and beautifully smooth. Taste it! This is your chance to adjust sweetness or spices. Does it need a little more cinnamon? A tiny pinch more sugar? Your call!
6. Prep for Baking: Preheat your oven to a cozy 375°F (190°C). While the oven is heating, lightly grease a 9x13 inch baking dish with a little butter or non-stick cooking spray. This prevents sticking and makes serving easier.
7. Spread the Dreamy Filling: Spoon the sweet potato mixture evenly into your prepared baking dish. Use the back of your spatula to smooth out the top. You want a nice, flat surface for those marshmallows later.
8. Initial Bake (Pre-Marshmallow): Pop the dish into the preheated oven and bake for 20-25 minutes. This allows the casserole to heat through, firm up slightly, and let those flavors meld together. You'll notice it bubbling gently around the edges.
9. Add the Marshmallow Topping: Carefully remove the casserole from the oven. Arrange the miniature marshmallows evenly over the top of the hot sweet potato mixture. Don't be shy here; you want a good, fluffy layer.
10. Final Bake & Golden Glow: Return the casserole to the oven for another 5-10 minutes. Watch it like a hawk during this stage! The marshmallows will puff up and turn a beautiful golden brown. If you want a more deeply browned or slightly charred topping, you can switch your oven to broiler mode for the last 1-2 minutes, but *do not walk away*. Marshmallows burn quickly under a broiler.
11. Cool and Serve: Once the marshmallows are perfectly toasted, take the casserole out of the oven. Let it sit for 5-10 minutes before serving. This cooling time allows the casserole to set a bit more and prevents you from burning your mouth. Dig in and enjoy that comforting, sweet goodness!