Preheat the oven to 350°F. Coat a 9x13-inch baking dish with nonstick cooking spray.
Place the sweet potatoes in a large pot and cover them with water. Bring the water to a boil over medium-high heat.
Reduce the heat to medium and cook for 15 to 18 minutes, or until the sweet potatoes are very tender.
Drain the sweet potatoes well.
Transfer the sweet potatoes to a large mixing bowl and mash until mostly smooth.
Add the maple syrup, melted butter, eggs, milk, vanilla extract, cinnamon, and salt. Whisk until evenly blended.
Spread the sweet potato mixture evenly in the prepared baking dish.
Add the pecans, brown sugar, flour, and cinnamon to a medium mixing bowl. Stir to combine.
Add the melted butter and stir until the topping is evenly moistened and crumbly.
Sprinkle the pecan topping evenly over the sweet potato mixture.
Bake for 25 to 30 minutes, or until the casserole is hot and the topping is lightly browned.
Let the casserole rest for 5 minutes before serving.
Notes
Tips and Tricks
Drain well - Let as much water as possible drain from the cooked sweet potatoes before mashing them.Mash to preference - Leave a few small pieces for a more rustic casserole, or mash until very smooth.Watch the topping - If the pecans begin browning too quickly near the end of baking, loosely cover the dish with foil.Plan ahead - The sweet potato filling can be prepared ahead and refrigerated in the casserole dish. Add the pecan topping shortly before baking.
Storing and Reheating
Refrigerator - Cover leftovers and refrigerate for up to 4 days.Oven - Cover the casserole loosely with foil and reheat at 350°F until heated through.Microwave - Reheat individual portions in the microwave until hot.Freezer - The casserole can be frozen, although the pecan topping may soften slightly after thawing. Store tightly covered for up to 2 months.