Chimney Grilled Cheese - Alton Brown

Ingredients

• 2 slices sourdough bread (boule) 1/2-inch thick
• vegetable oil (for spritzing newspaper)
• 1/2 cup grated sharp cheddar cheese
• 1/2 cup grated gruyere cheese
• 1/2 cup grated provolone cheese
• 1/2 teaspoon dry mustard
• 1/4 teaspoon smoked paprika
• pinch freshly ground black pepper
• 2 teaspoons extra-virgin olive oil, plus more for brushing
• 1/2 cup chopped yellow or white onion
• pinch kosher salt