Preheat oven to 375℉. Using a serrated bread knife, make 1-inch diagonal cuts through the loaf of bread, not cutting through to the bottom (leave the bottom of the crust intact!). Next, make diagonal cuts in the opposite direction, creating a "criss-cross" pattern.
Pour the melted butter into the crevices of the bread. Next, spoon the pesto into the crevices of the bread, spreading it around evenly. Add the chopped sundried tomatoes into the crevices of the bread. Lastly, push the cheeses down into the crevices of the bread. Some will end up just covering the top if you run out of room..this is ok! Sprinkle the top with the grated parmesan.