1. Prepare the ingredients by slicing four pieces of sourdough or artisan bread, then spread butter or olive oil on one or both sides of each slice to achieve a crispy crust.
2. Mix the cheese filling by combining shredded mozzarella, ricotta cheese, and optional Parmesan in a small bowl. Add a dash of garlic powder, Italian seasoning, or black pepper for extra flavor if desired.
3. Sauté or steam fresh spinach briefly, then drain and pat it dry to avoid excess moisture leading to a soggy sandwich.
4. Chop sun-dried tomatoes into small, bite-sized pieces to evenly distribute their tangy flavor in your sandwich.
5. Layer your sandwich by spreading the cheese mixture onto two slices of bread and topping with spinach, chopped sun-dried tomatoes, and optional pesto for added Mediterranean taste.
6. Finish assembling by placing the remaining slices of bread on top with the buttered or oiled side facing outward for optimal grilling and crunch.
7. Preheat a skillet or non-stick griddle over medium or medium-low heat to avoid burning and to evenly cook the bread and melt the cheese.
8. Grill the assembled sandwiches for 3 to 6 minutes per side, gently pressing with a spatula to ensure uniform browning and a creamy, melted interior.
9. Check readiness by ensuring the bread is golden brown and crispy, with the cheese fully melted. Lower the heat if needed to prevent burning during the process.
10. Remove the sandwiches from the skillet and slice them diagonally for an appealing presentation before serving.
11. Pair your grilled cheese with a side of soup such as tomato, vegetable, or roasted feta soup, or a fresh salad for a well-rounded, hearty meal.
12. For additional customization, incorporate ingredients such as roasted red peppers, caramelized onions, prosciutto, or a drizzle of balsamic glaze for extra flavor.
13. Store leftovers by cooling completely, then placing in an airtight container for up to two days in the refrigerator. Use parchment paper to separate layers if stacking.
14. Reheat by using a skillet or oven for optimal crispy texture and warm filling. Avoid microwaving as it may result in soggy bread.