Preheat oven to 350°F (175°C).
Prepare carrots by peeling and trimming stems, then arrange in a 9x13-inch baking dish.
Make glaze: In a mixing bowl, cream together butter, sugar, salt, and cinnamon using an electric mixer.
While the mixer is running, slowly add boiling water and orange juice until well combined into a smooth glaze.
Pour glaze over the carrots, cover tightly with aluminum foil, and bake for 90 minutes (check at 75 minutes if your oven runs hot).
Serve: Remove foil, transfer carrots to a serving platter, drizzle with melted cinnamon butter sauce, and garnish with parsley if desired.