Preheat oven to 350℉. Grease a 9x13 inch glass baking dish with cooking spray. Set aside.
Peel the sweet potatoes and cut into 1 ½-2 inch cubes. Place in a large pot with the apple cider and water. Bring to a boil over high heat. Once boiling, reduce heat slightly and boil for 20 minutes or until potatoes are easily pierced with a fork.
While potatoes are boiling, place the pecans on a baking sheet and toast for 8 minutes, stirring halfway to toast evenly. Remove from oven and cool slightly before chopping into small pieces. Set aside. Place the butter in a small saucepan. Melt, stirring often, and simmer over medium-low heat until the butter becomes fragrant and starts to brown. As soon as the butter turns a light brown color, transfer to a bowl to cool. Set aside.
Drain potatoes and cool 5 minutes. Mash them through a ricer and return to the pot they were cooked in, or return potatoes to the pot and mash with a potato masher.
Add half of the browned butter, eggs, cream, maple syrup, salt, and boiled cider to the mashed potatoes. Fold in with a rubber spatula until well-combined. Transfer to the prepared baking dish and smooth out the surface.
In a medium bowl, combine the chopped pecans, brown sugar, flour, cinnamon, and the remaining half of the browned butter. Stir to combine until the mixture resembles coarse sand. Sprinkle evenly on top of the potatoes.
Bake the potatoes for 30 minutes until heat through and the topping is crisp and golden. Serve hot.
Make-ahead option - cover the unbaked casserole and refrigerate overnight. Add an additional 10-15 minutes to the baking time.
Freezer option: cover the unbaked casserole tightly with plastic wrap and then a layer of foil. Freeze for up to 6 months. Thaw in the refrigerator overnight before baking. Add an additional 15-30 minutes to the baking time.