In a large skillet over medium-high heat, cook 1 1/2 pounds thinly sliced carrots in butter and 3/4 teaspoon each pumpkin pie spice, salt and pepper, 3 minutes. Stir in 1 cup water and 1 tablespoon each cider vinegar and dark brown sugar. Cover and simmer until tender, 12 to 14 minutes, stirring once. Add 1 tablespoon butter and simmer, uncovered, until glazed, 3 to 5 more minutes. Season with salt and pepper; top with pepitas.