Preheat oven to 400°F (200°C).
Peel the carrots, trim the ends, and slice them in half lengthwise. Place them in a large roasting pan or baking dish.
In a small bowl, whisk together the brown sugar, maple syrup, minced garlic, thyme, salt, and black pepper until combined.
Pour the maple mixture over the carrots and toss to coat evenly.
Lay the butter slices on top of the carrots.
Roast for 40–50 minutes, tossing once or twice during cooking, until the carrots are fork-tender and caramelized.
Remove from oven, toss one last time in the glaze, season to taste, and serve warm.