Preheat your oven to 375°F (190°C). Line a heavy rimmed baking sheet with aluminum foil and place a sheet of parchment paper on top.

Using a sharp serrated bread knife, slice the sourdough boule vertically into 1-inch thick columns, stopping about 1/2 inch before the bottom crust so the loaf stays fully intact. Turn the loaf 90 degrees and slice across in 1-inch intervals to create an even diamond grid pattern.

In a medium mixing bowl, beat softened cream cheese and sour cream until smooth. Fold in chopped artichoke hearts, thoroughly squeezed dry spinach, 1/2 cup parmesan, onion powder, and black pepper until completely blended.

In a small bowl, whisk together melted butter, minced garlic, chopped parsley, kosher salt, and crushed red pepper flakes.

Gently pry open the cuts of the sourdough loaf with your fingers. Use a small spoon to push generous dollops of the creamy spinach artichoke mixture deep into every crevice.

Tuck shredded mozzarella cheese generously into all the slits alongside the dip. Brush the entire exterior and drizzle deep into the cracks with the melted garlic herb butter. Sprinkle the top with remaining parmesan.

Wrap the loaf loosely with aluminum foil (tenting slightly so cheese does not stick to foil). Bake at 375°F (190°C) for 15 minutes until the cheese is completely melted deep inside.

Carefully open and peel back the foil to expose the top crust. Bake uncovered for an additional 7 to 10 minutes until the crust turns deeply golden and crunchy and the cheese bubbles with toasted browned spots.

Transfer to a serving board. Garnish with a shower of freshly minced parsley and red pepper flakes. Serve immediately while molten hot for epic cheese pulls!