In a saucepan with a lid, combine 2 pounds carrots (peeled and cut into ½-inch thick slices), 1 cup water, ¼ cup brown sugar, ½ teaspoon salt, and ¼ cup unsalted butter.
Place the saucepan over medium heat and bring the mixture to a gentle simmer, stirring once to dissolve the brown sugar.
Cover the saucepan, reduce the heat to low-medium, and simmer for 10 minutes, or until the carrots are tender when pierced and most of the liquid has reduced.
Uncover and cook 3–5 minutes more, stirring occasionally, until the remaining liquid thickens into a glossy glaze that coats the carrots.
Remove from heat, sprinkle with 1 teaspoon chopped fresh parsley if desired, and serve.