01 - 
                In a medium bowl, combine ricotta cheese, chopped sun-dried tomatoes, chopped spinach, and grated Parmesan cheese. Mix thoroughly and season with salt and black pepper to taste.
              
              
              
                02 - 
                Arrange sourdough bread slices on a clean surface. Spread a layer of ricotta mixture on one side of each slice.
              
              
              
                03 - 
                Sprinkle shredded mozzarella cheese evenly over the filling on half of the bread slices. Top each with a remaining slice, ricotta side in, forming sandwiches.
              
              
              
                04 - 
                Heat a large skillet over medium heat. Add 1 tablespoon olive oil and 1 tablespoon butter. Once butter is melted, place two sandwiches in the skillet.
              
              
              
                05 - 
                Grill sandwiches for 3–4 minutes per side or until bread is golden and cheese is fully melted. Repeat with remaining sandwiches, adding more olive oil and butter as needed.
              
              
              
                06 - 
                Transfer sandwiches to a board and let rest for 1 minute. Slice in half and serve warm.