Preheat your oven to 350°F and prepare a baking sheet.

Start by shredding the mozzarella cheese and chopping the pepperoni into small bite-sized pieces. Set both aside.

Using a sharp bread knife, carefully slice across the loaf of sourdough bread about 1 inch apart, making sure not to cut all the way through the bottom. Rotate the loaf 90 degrees and slice again, creating a crisscross pattern. This will form pockets throughout the bread that hold all the cheesy goodness.

Gently pull open the cuts and pack the shredded mozzarella and chopped pepperoni into the bread, making sure to distribute everything evenly throughout the loaf.

In a small bowl, melt the butter and stir in the Italian seasoning, dried parsley, and garlic salt. Use a pastry brush to generously brush the seasoned butter over the top of the bread, allowing it to drip down into the cuts.

Wrap the entire loaf loosely in aluminum foil and place it on your baking sheet. Bake covered for 30 minutes to allow the cheese to melt and everything to heat through.

After 30 minutes, carefully remove the foil and return the bread to the oven. Bake uncovered for an additional 10 minutes, or until the cheese is fully melted and the top is golden and bubbly.