In a medium bowl, combine ½ cup of chopped spinach, ¼ cup of chopped artichoke hearts, 1 tablespoon of cream cheese, and ¼ cup of shredded mozzarella. Mix well until evenly coated, seasoning with salt and pepper to taste.

Place a non-stick skillet over medium heat and allow it to warm up for about 2 minutes. Spread 1 tablespoon of butter evenly on one side of each slice of sourdough bread.

With the buttered sides facing out, spread a generous amount of the spinach artichoke mixture onto the unbuttered side of one slice. Top with the second slice.

Carefully place the sandwich in the preheated skillet and grill for 2-3 minutes on the first side until golden brown.

Using a spatula, gently flip the sandwich over and grill for another 2-3 minutes.

Once grilled, remove from skillet and allow to cool slightly before slicing in half. Serve hot.