Fill a large skillet or pan just over ¼ full with vegetable oil. Heat to 375°F.
Whisk the egg and water together in a large mixing bowl. Add flour, salt, and baking powder and whisk until smooth.
Arrange 2 slices of turkey, 2 slices of ham, and 2 slices of Swiss cheese evenly on 4 slices of bread. Place the remaining slices of bread on top of each sandwich.
Dunk each sandwich into the batter mixture. Coat all sides with batter.
Carefully place one sandwich at a time into the hot oil. Cook for 3 minutes on each side or until golden brown. Place the fried sandwiches on a paper towel-lined plate. Repeat with the other 3 sandwiches.
Sprinkle the hot sandwiches with powdered sugar.
Serve with raspberry preserves, grapes, and strawberries on the side. Enjoy immediately!