Assemble the Sandwiches
Lay out the bread slices. Spread a thin layer of mustard or mayo on one side of each slice if desired.
Add one slice of Swiss cheese, followed by 1–2 slices of ham and turkey, and top with another slice of cheese.
Place the second slice of bread on top to form a sandwich.
Prepare the Batter
In a shallow bowl, whisk together the eggs, milk, and flour until smooth. Add a pinch of salt and pepper for seasoning.
Dip the Sandwiches
Dip each sandwich into the batter, coating both sides evenly. Let any excess batter drip off.
Cook the Sandwiches
Heat a skillet or griddle over medium heat and add 1 tablespoon of butter.
Place the sandwiches in the skillet and cook for 3–4 minutes per side, or until golden brown and the cheese has melted. Add more butter as needed for additional sandwiches.
Serve
Transfer the sandwiches to a plate. Dust with powdered sugar and serve with a side of raspberry or strawberry jam for dipping.