Preheat oven to 400°F (200°C). Prick sweet potatoes all over with a fork, place on a foil-lined baking sheet, and roast for 45 to 55 minutes until fork-tender and caramelized. Allow to cool for 10 minutes, then slip off the skins.

Reduce oven temperature to 350°F (175°C). Grease a 9x13-inch (or 2.5-quart) ceramic baking dish with butter.

In a large mixing bowl, beat the warm sweet potato flesh with melted butter, brown sugar, whole milk, eggs, vanilla, cinnamon, nutmeg, and sea salt using a hand mixer on medium speed for 2 minutes until completely smooth, fluffy, and lump-free.

Spread the sweet potato mixture evenly into the prepared baking dish with a spatula.

In a medium bowl, stir together chopped pecans, dark brown sugar, flour, melted butter, cinnamon, and salt with a fork until moist, clumpy crumbs form.

Scatter the pecan streusel evenly across the entire surface of the sweet potato base, ensuring full edge-to-edge coverage.

Bake at 350°F (175°C) for 35 to 40 minutes, until the sweet potato custard is puffed and set in the center and the pecan streusel is bubbly, fragrant, and deeply caramelized.

Cool for 10 to 15 minutes before serving warm. Watch as the crunchy brown sugar pecan crust gives way to the velvety spiced sweet potato underneath!