Olive oil (for pan)
5 1/2 pounds sweet potatoes, peeled, cut into 1 1/2' pieces
2 teaspoons kosher salt, divided, plus more
1 1/4 cups pure maple syrup, divided
2 cups pecan halves (about 7 ounces)
1 1/2 teaspoons freshly ground black pepper, divided
                    

Preheat oven to 350°F. Oil a 3-qt. baking dish. Cook
potatoes in a large pot of boiling salted water until very
tender, about 12 minutes. Drain; let sit in colander 15
minutes. Meanwhile, heat 1/2 cup syrup in a large skillet
over medium-high. Add pecans, 3/4 tsp. salt, and 1 tsp.
pepper and cook, stirring constantly, until syrup has
evaporated and pecans are glazed, about 5 minutes. Transfer
to a parchment-lined rimmed baking sheet and let cool. Purée
potatoes, 1 1/2 cups water, and remaining 3/4 cup syrup, 1
1/4 tsp. salt, and 1/2 tsp. pepper in a food processor until
smooth. Transfer potato mixture to prepared baking dish.
Coarsely chop pecans and sprinkle evenly over potato
mixture. Bake casserole until top is lightly browned, about
40 minutes. Let sit 15 minutes before serving. Casserole can
be assembled, without topping, 2 days ahead; cover and
chill. Candied pecans can be made 2 days ahead; store in an
airtight container at room temperature.