Ultimate Grilled Cheese

INGREDIENTS

• 6 ounces aged Gruyere or Comte cheese
• 1/4 cup freshly grated Parmesan cheese
• 6 tablespoons salted butter, at room temperature
• 1/2 teaspoon freshly ground black pepper
• 1 cup good mayonnaise
• 12 slices thick-cut bacon, such as Nodine's applewood smoked
• 1 1/2 teaspoons kosher salt
• 6 ounces extra-sharp Cheddar, such as Cabot or Shelburne Farms
• 1 white pullman loaf or sourdough bread, sliced 1/2 inch thick (12 slices)
• 1/4 cup Dijon mustard