Grated white Cheddar and mozzarella on thick sourdough bread.
Preheat a tawa or cast iron pan over medium heat. Preheat oven to 275°F.
In a medium bowl, combine the grated white cheddar and mozzarella cheeses and season mixture with a pinch salt and pepper, and cayenne pepper if you so desire. Combine well and set aside.
For each grilled cheese sandwich, proceed as follows, cooking as many as you can without crowding the pan and not compromising even heat along the pans surface. Generously butter each slice of bread on one side, making sure to evenly cover the slice end to end, and season each buttered side lightly with salt and pepper. Place one slice, butter side down, onto heated cast iron pan. Spread 3⁄4 cup of cheese mixture evenly over the slice (make sure the cheese goes end to end) and top with second piece of bread, butter side up. Season top side of buttered bread with a pinch of salt and pepper. Cook low and slow, letting butter gently crisp up the bread until dark golden. (Be patient! This will take 4-5 minutes.) Carefully flip the sandwich over and continue to cook the other side, until cheese is nicely melted and the bread is crisp and golden on second side, another 4-5 minutes. Remove from heat and place on a baking sheet in low oven to keep warm while preparing remaining sandwiches.