Preheat oven to 375°. 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 butter, cream, 1 tsp. salt, and 1/2 tsp. pepper. Taste and add more salt and pepper if you like. Butter 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 at 375° until an instant-read thermometer inserted in center reaches at least 160°, 20 to 30 minutes. Uncover and bake until pecans are crunchy, 20 minutes more.
Make ahead: Through step 3, up to 1 day, chilled. Allow 45 to 60 minutes to heat (step 4) before uncovering.