Preheat oven to 200F. Using eight slices of bread for each, make two layered sandwiches, alternating bread and mozzarella. Cut and fit the mozzarella slices as necessary to cover the bread evenly. The cheese shouldn’t overhand bread slices, as the crusts will be trimmed before cooking. Cut the sandwich into 4 even squares, placing a skewer at the center of each square. Press gently while cutting to make compact sandwiches, trim crusts. Pour enough vegetable oil into a wide, deep skillet to fill it 1 1/2”. Heat over medium heat or until oil registers 350F on a deep frying thermometer. Line a baking sheet with paper towels and set side. Meanwhile, in a shallow bowl, whisk eggs, milk, salt and pepper until combined. In a separate bowl, fill with flour. Dredge each skewered square into flour, coating all sides, then dip into the egg mixture. Fry, turning as necessary, until golden brown on all sides. Frying should take approximately 4 minutes. Drain sandwiches on paper towel lined pan and place in warm oven. Repeat with all sandwiches.