Combine basil, pine nuts (if using), garlic, lemon, and salt in a food processor until well incorporated (15-30 seconds).
While the motor is running, slowly add in olive oil, then cheese until the mixture resembles a thick paste.
Add pepper to taste.
Pesto can be stored in an airtight container in the fridge for up to 2 weeks.
Heat up a large skillet to medium high heat.
Spread pesto on the inside of each sandwich (approximately 2 tsp per side).
Place 2 slices of havarti between two slices of bread, and add a few artichoke heart leaves.
Butter one side of the bread, and place butter side down on the skillet. Lower heat to medium.
Cook the first side for approximately 5 minutes or until golden brown. Butter the top slice before switching sides.
Cook on the second side for about the same time, or until cheese is melted.
Cut in half and serve immediately.
