Yes you can use frozen carrots - it would be a time saver, though they won't be firm if you like them that way. For best results you'll want to thaw them for about an hour before using, as they'll cook more evenly. If you can't do that, you can place the frozen carrots in a colander and run water from the tap over them for 5-10 minutes. Then proceed with the recipe, checking at an earlier time for doneness, though, since the frozen carrots might not need as long.