Spinach Dip Hot Bread

The classic spinach dip appetizer achieves new heights in this irresistibly cheesy appetizer.

This gooey, cheesy appetizer is perfect for watching the game, alongside a salad or bowl of soup, or on a lazy weekend afternoon. The toasty sliced sourdough boule is filled with buttery bechamel sauce and spinach, but the real star is the Calabrian chiles, which lend each bite a gentle kick of heat. Feel free to customize this depending on the bread you have on-hand; it works nicely with a baguette, too.

• ¼ cup plus 2 tablespoons unsalted butter, divided
• 2 tablespoons all-purpose flour
• ¾ cup whole milk
• ¾ cup heavy whipping cream
• 1 ¼ teaspoons kosher salt, divided
• ¾ teaspoon ground white pepper, divided
• 1 ½ cups chopped yellow onion (from 1 medium [10-ounce] onion)
• 1 (10-ounce) package fresh baby spinach (about 8 cups)
• 14 ounces pre-shredded Parmesan cheese (about 4 1/4 cups)
• 1 (24-ounce) sourdough boule
• 1 tablespoon chopped jarred Calabrian chiles
• 1 ½ ounces pre-shredded low-moisture part-skim mozzarella cheese (about 1/3 cup)