Preheat oven to 200°C / 400°F and line a large baking sheet with parchment paper.
Wash, peel, and trim the carrots, then slice any thicker ones lengthwise for even cooking.
In a mixing bowl, toss carrots with olive oil, melted butter, maple syrup, salt, and pepper until evenly coated.
Spread carrots in a single layer on the prepared sheet; do not overcrowd.
Roast for 25–35 minutes, turning halfway through, until tender with slightly blistered edges.
Once caramelized, sprinkle fresh thyme and lemon zest; toss lightly before serving warm.