Step 1

In the bowl of a food processor fitted with the steel blade, combine the sun-dried tomatoes with their oil, garlic, salt, red pepper flakes, sugar, basil, pine nuts, Parmigiano-Reggiano and 2 tablespoons of water. Pulse, scraping down the sides as necessary, until the mixture is finely puréed.

Step 2

Spread one side of each slice of bread with butter, then flip over and spread the pesto evenly over the other side of each slice. Heat a large nonstick or cast iron pan over medium heat. Place 4 slices of bread, butter-side-down, in the pan. Divide the cheese evenly over the bread, then top the sandwiches with the remaining bread. Cook until the first side is golden brown, a few minutes. Carefully flip the sandwiches and cook until the cheese is fully melted and the bread is golden brown, a few minutes more. Let cool slightly, then slice the sandwiches in half and serve.

Step 3

Note: You'll have plenty of leftover sun-dried tomato pesto. It keeps well in the refrigerator for up to 4 days and can be frozen for up to 2 months. You can also try tossing the pesto with pasta; just keep in mind that the pesto is thick so you'll need to thin it with some of the pasta cooking water and a little olive oil when tossing it with the pasta.