For a smoother guacamole, use a food processor. But be careful not to over-process, or it will become too liquidy. Adjust the amount of jalapeño to your spice preference. Remove the seeds and membranes for less heat. For an extra layer of flavor, try adding a pinch of cumin or smoked paprika to the guacamole. If you don't have Havarti cheese, Monterey Jack or Pepper Jack are great substitutes. Don't overcrowd the pan; cook the sandwiches in batches if necessary to ensure even browning.