In the bowl of a stand mixer fitted with the paddle attachment, beat 1 cup flour, brown sugar, yeast, salt, and cinnamon at low speed just until combined.
In a small saucepan, heat butter, sour cream, and 2 tablespoons water over medium heat, stirring frequently, until butter is melted and mixture registers 120° to 130° on an instant-read thermometer. Add butter mixture to flour mixture; beat at medium speed for 2 minutes, stopping to scrape sides of bowl. Add sweet potato and eggs; beat for 1 minute, stopping to scrape sides of bowl. With mixer on low speed, gradually add remaining 2½ cups flour, beating until combined.
Switch to the dough hook attachment. Beat at medium-low speed until a soft, slightly sticky dough forms, 10 to 12 minutes. (Dough might stick slightly to bottom and sides of bowl but should not stick to sides.)
Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°) until doubled in size, about 1 hour.
Punch down dough; cover and let stand for 10 minutes. On a lightly floured surface, roll dough to a 14×12-inch rectangle.
For filling:
In a small bowl, stir together brown sugar, pecans, and cinnamon. Spread butter onto dough; sprinkle brown sugar mixture onto butter, leaving a ¼-inch border on one short side. Starting at short side without border, roll up dough into a log, pinching seam to seal. Cut log into 9 (1⅓-inch-thick) slices.
For topping:
In a small saucepan, heat brown sugar, cane syrup, and butter over medium heat, stirring frequently, until sugar is melted and mixture is smooth. Remove from heat; stir in vanilla.
Spray a 10-inch cast-iron skillet with baking spray with flour. Pour topping into skillet, swirling to coat bottom and sides. Sprinkle pecan halves in bottom of skillet. Place dough slices, cut side up, on pecans. Cover and let rise in a warm, draft-free place (75°) until puffed, 25 to 30 minutes.
Preheat oven to 350°.
Bake until golden brown, 25 to 30 minutes. Remove from oven, and let cool on a wire rack for 10 minutes. Carefully invert buns onto a serving platter; serve warm.
Recipe by Southern Cast Iron at https://southerncastiron.com/sweet-potato-sticky-buns/