Cook the sweet potatoes. Add peeled and cubed sweet potatoes to a large pot of salted water. Bring to a boil and cook for 15–20 minutes, until fork-tender. Drain thoroughly and allow to steam dry for a few minutes.
Brown the butter. Melt ½ cup butter in a light-colored skillet over medium heat. Cook, stirring occasionally, for 4–6 minutes until golden brown with toasted milk solids and a nutty aroma. Immediately transfer to a heatproof bowl.
Whip the sweet potatoes. Add cooked sweet potatoes to a food processor with about two-thirds of the browned butter, warmed heavy cream, maple syrup, cinnamon, nutmeg, salt, and vanilla if using. Blend until silky smooth, taking care not to overprocess. Taste and adjust seasoning.
Make the pecans. Melt 2 tablespoons butter in a skillet over medium heat. Add pecans and toast for 2–3 minutes. Stir in maple syrup, hot honey, and rosemary. Cook another 1–2 minutes until glossy and coated. Sprinkle with flaky sea salt and spread onto parchment to cool slightly.
Assemble. Spoon whipped sweet potatoes into a shallow serving bowl, creating swirls with the back of a spoon. Drizzle with remaining brown butter.
Finish and serve. Spoon the hot honey pecans over the sweet potatoes. Top with fresh rosemary, flaky sea salt, and an additional drizzle of hot honey. Serve warm.