Melt 1/2 stick (4 tablespoons) of the butter in a large skillet (with a lid) over high heat. Add half the carrots and stir them around to brown them quickly, about 1 minute. Remove to a plate and repeat with the remaining carrots.
Pour the whiskey into the skillet, taking care if you're cooking over an open flame. Let the whiskey bubble up and cook until slightly reduced, about 3 minutes. Reduce the heat to medium low, add the other 1/2 stick of butter and stir it around until it's melted. Stir in the brown sugar and some salt and pepper. Add the leaves from 1 of the sprigs of thyme, then add the carrots. Reduce the heat to low, place the lid on the skillet and cook for 5 minutes. Remove the lid and cook for another 5 minutes.
Serve garnished with the remaining thyme sprig.