Prep time: 45 minutes
Total time: about 1 hour 30 minutes
5 lb sweet potatoes, cut into chunks
1 1/4 tsp salt, divided, plus more for boiling potatoes
15 to 20 coarsely broken gingersnap cookies
1/2 cup flour
1/2 cup brown sugar
1/2 cup butter, cut into bits
1/2 cup maple syrup
1/2 cup half-and-half
2 tsp vanilla extract
1/2 tsp cinnamon
1/4 tsp ground nutmeg
2 large eggs
Coat a 9 by 13-inch baking dish with cooking spray.
Place potatoes in a large pot, cover with water, and add a generous pinch of salt. Bring to a boil, reduce heat, and simmer until potatoes are very tender, 14 to 16 minutes. Drain and set aside to cool.
Meanwhile, make the topping. Put the gingersnaps, flour, sugar, and 1/4 tsp salt in a food processor; pulse once or twice to combine. Add the butter and pulse a few more times. (The cookies should still be in small chunks.)
Once the potatoes are cool, remove the skins. Make into a chunky puree in a blender, food processor, or by hand using a potato masher.
In a large bowl, whisk together the maple syrup, half-and-half, vanilla, cinnamon, nutmeg, eggs, and remaining 1 tsp salt. Add the potato puree; mix thoroughly. Transfer to baking dish. Sprinkle the topping evenly over the dish. [May be covered in several layers of plastic wrap and frozen for up to three weeks. Thaw in the refrigerator overnight, bring to room temperature, and continue.]
Preheat oven to 350°F. Bake for 45 minutes, or until the top is lightly browned.