6 pounds orange-fleshed sweet potatoes
1/4 cup melted margarine plus 3 tablespoons cut into pieces and more for greasing dish
1/2 cup pareve whipping cream
About 1 teaspoon kosher salt
About 1/2 teaspoon pepper
1 cup chopped pecans
3 tablespoons maple syrup
Preheat oven to 375°F. Bake sweet potatoes on a rimmed baking sheet until very tender when pierced, 1 1/4 hours.
Cut sweet potatoes in half and let cool a bit. Scoop out flesh and beat half of them at a time in a stand mixer, using paddle attachment on medium speed, until very smooth, about 3 minutes.
In a large bowl, stir together sweet potatoes, melted margarine, pareve cream, 1 tsp. salt, and 1/2 tsp. pepper. Taste and add more salt and pepper if you like. Grease a 3-qt. baking dish. Add sweet potatoes and smooth surface. Top with pecans, maple syrup, and butter pieces. Cover dish with parchment paper cut to fit, then foil.
Bake for 20 to 30 minutes. Uncover and bake until pecans are crunchy, 20 minutes more.