Twelve croissants are baked first; the remaining 10 can be frozen. The croissants take at least 10 hours to make from start to finish, but the process can be spread over two days. Use high-protein all-purpose flour, such as King Arthur, and European-style butter (we like Plugrá). If the dough retracts or softens at any point, fold it into thirds, wrap it in plastic, and freeze it for 15 minutes. Do not make these in a room that is warmer than 80 degrees. Prep time includes rise time.