Step 1

Preheat the oven to 350°F. Butter a 2-quart casserole dish. Line a baking sheet with aluminum foil.

Step 2

Pierce each sweet potato several times with a paring knife or fork and place on the baking sheet. Bake for 60 to 70 minutes, or until soft and tender when pierced with a paring knife. Transfer the baking sheet to a cooling rack. Cut a slit in the potatoes lengthwise and cool for 15 to 20 minutes.

Step 3

Scoop the sweet potato flesh into a large bowl and mash it with a potato masher or fork. Add the butter, sugar, and cream and, using an electric mixer on medium-high speed, beat to blend. Add the eggs, one at a time, and beat to combine. Add the vanilla, salt, and allspice and beat until evenly mixed. Spread the mixture in the casserole dish.

Step 4

Make the topping (instructions below), then bake for 45 minutes at 350°F, or until the ingredients are puffed slightly and the topping is a rich light brown. Transfer to a cooling rack for 15 to 20 minutes before serving.

Step 5

Combine the brown sugar, flour, cinnamon, salt, and butter in a food processor and pulse briefly.

Step 6

Add the pecans and spread the topping evenly over the sweet potato mixture.