Heat oven to 350 degrees. Peel carrots. Trim stem end, leaving ¼ inch of green attached. Cut into 1-inch-long pieces. In a medium-size ovenproof pan, melt butter over medium heat. Toss carrots in butter; then place in oven for 20 minutes. Remove pan from oven and toss carrots with thyme. Return pan to oven and roast another 15 minutes, or until carrots are tender; as they cook, the butter will slowly caramelize. Season with salt and pepper to taste.