Step 1

To a large stockpot, add the sweet potato chunks, cover with water, and bring to a boil. Cook over high heat until sweet potatoes are fork tender; about 20 minutes. Drain well and transfer to a large bowl.

Step 2

Preheat oven to 350F and spray a 3 to 4-quart baking or casserole dish or a 9×13-inch baking pan with cooking spray; set aside.

Step 3

To the large bowl with the sweet potatoes, add the eggs, butter, milk, brown sugar, granulated sugar, vanilla, salt, optional nutmeg, optional cinnamon, and beat with a handheld electric mixer on medium-high speed until combined and fluffy. Alternatively, if you prefer a coarser texture that's more chunky, you can use a potato masher.

Step 4

Turn out into baking dish, smoothing the top lightly with a spatula; set aside.

Step 5

To a large microwave-safe bowl, add the butter and heat on high power to melt, about 1 minute.

Step 6

Add the brown sugar, flour, salt, and gently toss with a fork (or your fingers) until moist crumbs form.** (See Notes for Tips)

Step 7

Add the pecans and gently toss to incorporate.

Step 8

Evenly turn topping out over filling.

Step 9

If making ahead of time - stop now. Cover tightly with foil, and refrigerate for up to 24 hours. If you've made it ahead, allow the sweet potato casserole to sit out at room temp for 30 to 60 minutes. Don't put it straight into the oven from the fridge because the baking time will be altered.

Step 10

Bake the sweet potato casserole for about 40 to 45 minutes; start checking at 30 minutes. Bake until top is lightly golden browned, set on the edges, and mostly set in the center. Tip - Place baking dish on a sheet pan to catch any accidental overflow to save on cleanup later.

Step 11

Remove the casserole from the oven, evenly sprinkle with the marshmallows, and bake for 5 minutes more, or until the marshmallows are lightly golden browned. Tip -Keep a very watchful eye on the marshmallows since they are prone to burning. Set a timer so you don't accidentally forget about it.

Step 12

Serve immediately. Extra will keep airtight for up to 1 week in the fridge and up to 4 months in the freezer.***(See Notes)