Caramelized Onion and Garlic Bread

Bahan-bahan (1 porsi)

• 2 heads garlic, cloves smashed and peeled, divided
• 1/2 small sweet onion, sliced
• 10 tablespoons (1 1/4 sticks) unsalted butter
• 1 loaf ciabatta or Italian bread
• 1/4 cup fresh basil, roughly chopped
• 1/4 cup fresh parsley, roughly chopped
• Kosher salt, to taste
• Red pepper flakes, to taste, optional
• 1/4 cup freshly grated parmesan cheese, plus more to serve