Preheat your oven to 375°F (190°C). Line a large rimmed baking sheet with parchment paper.

Using a serrated bread knife, slice off the top 1 1/2 inches of the sourdough boule like a lid. Cut around the interior perimeter, leaving a sturdy 3/4-inch bread wall and base.

Use your hands to gently hollow out the soft interior bread into bite-sized 1-inch cubes. Place the hollowed bread bowl and the bread cubes onto the baking sheet. Brush the interior of the bowl and the bread cubes with melted butter and a dust of garlic powder.

Critical moisture step: Wrap thawed spinach in a clean kitchen towel or cheesecloth and squeeze aggressively over the sink until zero excess liquid drips out.

In a large mixing bowl, beat softened cream cheese, sour cream, mayonnaise, minced garlic, kosher salt, black pepper, and red pepper flakes with a spatula until smooth and creamy.

Fold in the squeezed dry spinach, chopped artichoke hearts, 1 cup of mozzarella, and 1/2 cup of Parmesan cheese until evenly distributed.

Spoon the luscious dip mixture into the hollowed sourdough bread bowl, mounding it gently toward the center. Top with the remaining 1/2 cup of mozzarella and 1/4 cup of Parmesan cheese.

Cover the filled bread bowl loosely with a tent of aluminum foil to keep the bread crust from getting overly dark. Bake for 20 minutes.

Remove the foil tent, arrange the reserved sourdough bread cubes around the bowl on the baking sheet, and bake uncovered for another 8 to 10 minutes until the top cheese is bubbling vigorously and toasted with golden brown spots, and the bread cubes are crunchy crostini.

Optional broil: Broil on HIGH for 1 to 2 minutes for extra caramelized cheese blisters. Keep a watchful eye!

Garnish with freshly chopped parsley and freshly cracked black pepper. Transfer to a serving platter and serve immediately with toasted bread cubes, crisp celery, and sweet baby carrots!