Filling:

Cup of Yum
1. To a large stockpot, add the sweet potatoes, cover with water, and bring to a boil. Cook over high heat until sweet potatoes are fork tender. Drain in a colander (really shake out the water well) and transfer to a large bowl.
2. Preheat oven to 350F and spray a 3-quart baking dish or a 9×13-inch baking pan with cooking spray; set aside.
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 smooth.
4. Turn out into the baking dish, smoothing the top lightly with a spatula; set aside.
5. If making ahead, stop here, cover, refrigerate, and pick up with step 4 just before you're ready to bake it off the next day.

Topping:

1. To a large, microwave-safe bowl, add the butter and heat on high power to melt, about 1 minute.
2. Add the brown sugar, flour, salt, and toss with a fork until large crumbles form; set aside.
3. To the canister of a high speed blender or food processor, add the chips and pulse very briefly (about 10 seconds) to lightly crush them. The chips should be in small pieces, do not pulverized them into dust. Alternatively, you can transfer the chips to a large ziptop bag, seal it, and lightly beat it with a knife or roll a rolling pin (or wine bottle) over the bag as necessary to crush the chips.
4. Add the chips to the topping mixture and toss to incorporate.
5. Evenly turn topping out over filling and bake for about 40 minutes, or until top is lightly golden browned and set. If you chose to make-ahead, you will likely need to bake for about 50 minutes because you're starting with a cold casserole dish from the fridge.
6. Serve immediately.