Step 1: Heat oil in a large skillet over medium heat. Add carrots and season with salt and pepper; stir to coat with oil. Let cook for 3 minutes, then add brown sugar and molasses; stir to coat. Cook until carrots are tender and sauce is thick, 5 to 8 minutes, adding 1/2 to 1 cup water as necessary to prevent sugar from burning.
Step 2 : Meanwhile, heat grapeseed oil in a small skillet over medium-high heat. Add reserved carrot tops and cook until crisp. Transfer to a paper towel-lined plate and set aside.
Step 3: Add butter and rosemary to skillet; cook until butter is melted. Remove rosemary and discard. Transfer carrots to a serving dish and sprinkle with reserved fried tops.