Place the mustard and mayonnaise in a bowl and mix to combine. Spread ½ tablespoon over each slice of brioche. Mix to combine the cheeses. Top 4 slices with 1/3 cup of the cheese. Cut each sandwich in half. Place the eggs and milk in a bowl and whisk to combine. Sprinkle with sea salt and cracked black pepper. Dip the sandwiches in the beaten egg mixture. Wrap each finger with a slice of prosciutto. Heat 1 tablespoon oil in a large non-stick frying pan over a medium heat. Add the fingers and cook in batches for 2 – 3 minutes each side or until golden. Makes 8