The World's Most Carrot-y Carrots

Preheat sous-vide precision cooker to 183°F. Place carrots, butter, sugar, and 1/2 teaspoon kosher salt in a vacuum bag and seal according to manufacturer's instructions. Cook carrots in the water bath until fully tender, about 1 hour. At this point, carrots can be stored in refrigerator for up to 1 week. 

Empty entire contents of bag into a 12-inch, heavy-bottomed skillet and cook over high heat, stirring constantly, until liquid has reduced to a shiny glaze, about 2 minutes. Season to taste with salt and pepper, stir in parsley, and serve. If glaze breaks and turns greasy, add water a teaspoon at a time, shaking pan to re-form glaze.