In an 8x8-inch baking dish, combine the flour, baking soda and salt. In a separate bowl, whick together the eggs, water and milk, then add to the flour mixture. Whisk thoroughly until smooth and no lumps of flour remain, then set aside.

On each of 4 slices of bread, arrange one slice of ham, turkey, and swiss. Top with the remaining bread slices, then using a sharp knife, slice each sandwich in half on the diagonal. You may wish to insert toothpicks to hold everything together until the sandwich is fried.

Heat oil over medium-high heat to between 365-375 degrees. If the oil starts to smoke, turn the temperature down. Working carefully, dip half of each sandwich into the prepared batter, lift out and allow excess batter to drip off, then lower gently into the hot oil. Repeat with the other half of the sandwich. Work in batches and do not crowd the pan.

Cook in the oil for about 3 minutes, then flip and cook the other side of the sandwich for another 3 minutes, until golden brown on both sides.

Gently remove each diagonal sandwich half from the hot oil using tongs and set on a paper-towel lined baking sheet. Place in a warm oven until ready to serve. Repeat the process with the remaining three sandwiches, frying each sandwich one at a time and allowing the oil temperature to come back up between each batch.

When ready to serve, dust each sandwich with powdered sugar and serve with raspberry or blackberry jam on the side.