Preheat the oven to 450 degrees F. Line a baking sheet with parchment.
Put the carrots on the prepared baking sheet in a single layer. Pour 2 tablespoons of the butter over the carrots and sprinkle with 1/2 teaspoon each salt and pepper. Toss to coat. Bake until the carrots are browned and soft, 20 to 25 minutes.
While the carrots are baking, add the oil, molasses, cider vinegar, 1/2 teaspoon pepper, a pinch of salt and the remaining butter to a saucepan. Heat until melted, bubbling and slightly thickened, about 3 minutes. Set aside.
Transfer the carrots to a serving platter, drizzle with the molasses glaze and sprinkle with the mint and pecans.