1. Prepare Your Bread and Butter: Lay out your sourdough slices on a clean surface. Generously spread softened butter on one side of each slice of bread. This buttered side will be the exterior of your sandwich, ensuring a golden, crispy crust.

2. Assemble the First Layer: Place four slices of bread, butter-side down, into a large non-stick skillet or on a griddle over medium heat. Immediately top each of these slices with two slices of your chosen cheese.

3. Add Fresh Fillings: On top of the cheese, arrange a few thin slices of fresh tomato. Sprinkle the fresh basil leaves evenly over the tomatoes. Season lightly with salt and freshly ground black pepper.

4. Complete the Sandwich: Place the remaining four slices of sourdough bread on top, butter-side up. Gently press down on each sandwich with a spatula to ensure good contact with the pan.

5. Grill to Golden Perfection: Cook for 3-5 minutes on the first side, or until the bread is golden brown and the cheese is starting to melt. You can peek underneath to check the color.

6. Flip and Finish: Carefully flip each sandwich using a wide spatula. Cook for another 3-5 minutes on the second side, until that side is also golden brown and the cheese is fully melted and gooey. If the bread is browning too quickly, reduce the heat slightly.

7. Serve Immediately: Once cooked, remove the grilled cheese sandwiches from the pan. Let them rest for a minute or two, then slice them in half diagonally and serve hot.