In a skillet large enough to hold the carrots, heat the olive oil over medium heat. When the oil begins to smoke lightly, add the carrots and season with salt and black pepper. Using a wooden spoon, stir the carrots to coat with the oil and seasonings.
After the carrots have cooked for a few minutes, add the brown sugar and molasses
and continue to cook, stirring from time to time. Add a little water so they can become tender without burning the sugar. Continue to cook until tender, about 5 to 8 minutes. Add more water, if needed, but the sauce
should be thick enough to coat the carrots and should bubble around the edges of the pan. The carrots should be tender and fairly yielding when pierced with the tip of a knife. Add the butter and the rosemary
sprig. Once the butter has melted remove the rosemary sprig and discard. Transfer the carrots to a serving bowl and garnish with chopped carrot tops. Serve immediately or allow to "rest" a little before serving.