Ingredients

• 3 3/4 ounces thinly sliced pepperoni
• 16 medium white button mushrooms, sliced
• 3 cloves garlic, finely chopped
• 1 small red onion, sliced 1/8-inch thick
• 1 teaspoon dried oregano
• Kosher salt
• 6 cups low-sodium chicken broth or stock
• One 32-ounce jar marinara sauce
• 1/4 cup grated Parmesan, plus more for serving
• 4 slices sourdough whole wheat bread, halved
• 1 tablespoon olive oil
• 1 1/2 cups shredded mozzarella
• 1/4 cup torn fresh basil leaves, for serving, optional

Instructions

1. Add the pepperoni to a soup pot over medium-high heat and cook, stirring occasionally, until the pepperoni render their fat and get crispy, 3 to 4 minutes. Remove the pepperoni with a slotted spoon and drain on paper towels. Set aside.
2. Lower the heat to medium; add the mushrooms, garlic, onions, oregano and 1 teaspoon salt. Cook, stirring, until the vegetables soften and the mushrooms release their liquid, 6 to 7 minutes. Add the broth, marinara sauce and Parmesan; cover the pot and bring to a boil. Reduce the heat to medium and cook, about 15 minutes.
3. Position an oven rack in the center of the oven and preheat the broiler to medium-high. Put the bread on a baking sheet. Brush the bread with the oil and sprinkle with 1/4 teaspoon salt. Broil the bread until crisp and brown, 1 to 2 minutes. Flip the bread and sprinkle with 1 cup mozzarella. Broil until the mozzarella melts and is brown and bubbly, about 2 minutes.
4. Ladle the soup into 8 serving bowls. Sprinkle each bowl with the remaining 1/2 cup mozzarella, then top each with a bread half, melted-cheese-side up, and some of the pepperoni. Sprinkle with some Parmesan and basil if desired.