Begin by placing two thick slices of fresh sourdough bread on a clean surface. Generously spread butter on the top sides of each slice, ensuring complete coverage for that golden crust. Then, flip the slices over so the buttered sides are facing down and set them aside while you gather your remaining ingredients.

In the same pan used for the bread, start layering your pesto grilled cheese. On each slice of bread, add 3-4 slices of mozzarella cheese, ensuring an even distribution. Next, spread a tablespoon of basil pesto over the cheese, followed by sun-dried tomatoes and bacon if you choose to include it. Top each with another layer of mozzarella for extra creaminess before closing with the other slice of bread.

Gently press the assembled sandwiches down with a spatula, helping to compress the fillings and ensure everything stays in place. Spread more butter on the top side of each slice to guarantee a beautiful, crispy finish while cooking. This step is crucial for achieving that delightful crunch on your pesto grilled cheese.

Heat your pan over medium-low heat, ensuring it’s not too hot. Carefully place the sandwiches in the pan and let them cook for about 3-5 minutes per side. Keep an eye out for a golden-brown hue forming on the bread; this means it’s time to flip. The goal is melted mozzarella inside and a perfectly crispy crust outside.

Once both sides are beautifully browned, remove the sandwiches from the pan. Allow them to cool slightly before cutting them in half to showcase the gooey, melty interior. Serve your delicious pesto grilled cheese with a side of warm tomato soup or a fresh arugula salad for a complete, comforting meal.