📖 Instructions

1. First things first, grab your sweet potatoes. Give 'em a good scrub under cold running water to get rid of any dirt. Then, very carefully, peel all of them. Once they're peeled, you'll want to chop them into roughly 1-inch cubes. Try to make them as uniform in size as possible; this helps them cook evenly.
2. Place your cubed sweet potatoes into a large saucepan or pot. Cover them with cold water – just enough so they're submerged. Add a generous pinch of salt to the water, which helps season the potatoes from the inside out. Bring the water to a rolling boil over medium-high heat, then reduce the heat to medium-low and let them simmer. Cook for about 15-20 minutes, or until the potatoes are really fork-tender. This means when you stick a fork into a piece, it goes in with absolutely no resistance.
3. Once they're perfectly tender, carefully drain the sweet potatoes using a colander. Make sure to get rid of as much water as you can. Transfer the hot, drained potatoes back into the empty saucepan or a large mixing bowl. Now's the time for mashing! Use a potato masher to thoroughly mash the sweet potatoes until they’re smooth. If you like a *really* smooth texture, you could even use an electric hand mixer at a low speed. Be careful not to overmix if using an electric mixer, or they can get a bit gummy.
4. While the potatoes are still warm, add in the unsalted butter. The warmth of the potatoes will help it melt beautifully. Stir it in until it's completely incorporated and the potatoes look rich and glossy.
5. Now, let's get those flavors humming! Add the granulated sugar, light brown sugar, whole milk, vanilla extract, ground cinnamon, ground nutmeg, and a tiny dash of salt (remember, we already salted the boiling water, so just a pinch to balance the sweetness). Stir everything together really well with your rubber spatula or a sturdy spoon until all the ingredients are fully combined and the mixture is smooth and consistent. Take a little taste here – is it sweet enough for you? Does it need a tiny bit more spice? Adjust to your preference.
6. Lightly beat the large eggs in a small seperate bowl, then pour them into the sweet potato mixture. Stir them in quickly and thoroughly. The eggs are key for that truly soft, almost custardy center we're aiming for. They help bind everything and create a beautiful, tender texture as it bakes.
7. Preheat your oven to 375°F (190°C). Grab your 9x13 inch baking dish and lightly grease it with butter or cooking spray. This prevents sticking and makes serving so much easier.
8. Pour the sweet potato mixture evenly into your prepared baking dish. Use your spatula to spread it out smoothly. You want an even layer so it bakes consistently.
9. If you're using marshmallows, arrange them in a single layer over the top of the sweet potato mixture. You can use mini marshmallows for full coverage or larger ones for a more dramatic, gooey look. Don't worry if there are a few gaps; they'll puff up and melt together.
10. Place the baking dish into your preheated oven. Bake for about 25-30 minutes. If you're using marshmallows, keep a close eye on them during the last 5-10 minutes. You want them to turn a lovely golden brown and get wonderfully puffed up and gooey. If they're browning too quickly, you can loosely tent the casserole with aluminum foil.
11. Once baked, remove the casserole from the oven. Let it sit and cool for about 10-15 minutes before serving. This cooling time is super important – it allows the casserole to set up slightly and makes it easier to scoop. Serve warm and enjoy every single delicious, velvety bite!