Heat the oven to 425°F. Line a large rimmed sheet pan with parchment paper.
Pat the carrots completely dry. In a large bowl, toss them with the olive oil, salt and pepper until evenly coated, then spread in a single layer on the pan (use two pans if they are crowded).
Roast for 15 minutes, until the edges begin to brown.
Meanwhile, stir the maple syrup, melted butter and thyme together in a small bowl.
Pull the pan out, drizzle the maple mixture over the carrots and toss with a spatula to coat. Spread them back into a single layer and return to the oven for 10 minutes, until fork-tender and the glaze is bubbling and caramelized at the edges. Watch the last few minutes closely — maple can scorch at 425°F.
Transfer to a platter, spoon any pan glaze over the top, scatter with extra thyme and serve warm.
