Preheat the oven to 425 degrees. Line a large baking sheet with parchment paper or lightly grease it.
Add the baby carrots to a large bowl.
Melt the butter, then stir in the dark brown sugar, cinnamon if using, kosher salt, black pepper, and water until combined.
Pour the brown sugar mixture over the carrots and toss until evenly coated.
Spread the carrots in a single layer on the prepared baking sheet.
Roast for 20 minutes, then stir the carrots and return them to the oven for another 8 to 10 minutes, or until tender and caramelized around the edges.
Toss the hot carrots in the glaze in the pan before serving.