Preheat your oven to 400°F (200°C). Pierce whole sweet potatoes several times with a fork, place on a rimmed baking sheet lined with foil, and roast for 50 to 60 minutes until completely tender and caramelized when pierced with a knife. Allow to cool until safe to handle, then peel the skins away (they will slide right off).

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

In a large mixing bowl or bowl of a stand mixer fitted with the paddle attachment, beat the roasted sweet potatoes until completely smooth and free of lumps. Beat in the melted butter, milk or cream, dark maple syrup, dark brown sugar, cinnamon, nutmeg, salt, and vanilla extract until luxuriously blended.

Stir in the beaten eggs just until fully incorporated. Pour the smooth sweet potato mixture into the prepared ceramic baking dish, smoothing the top into an even layer with an offset spatula.

In a separate medium bowl, prepare the crunchy streusel: combine chopped pecans, dark brown sugar, all-purpose flour, ground cinnamon, and flaky sea salt. Pour in the 6 tablespoons of melted butter and stir with a fork until moist, clumpy, pebbly crumbs form.

Evenly scatter the pecan streusel crumble across the entire sweet potato base, pressing lightly so it adheres. Bake uncovered at 350°F (175°C) for 35 to 40 minutes until the edges are gently puffed, the sweet potato filling is set, and the pecan streusel is deeply golden, fragrant, and caramelized.

Remove from the oven and let rest for 15 minutes before serving warm. The resting time allows the soufflé-like sweet potato base to settle and the pecan streusel to crisp up to maximum crunchiness!