It's essentially French toast turned into a sandwich — two slices of stale bread are glued together with jam or ham, dipped in egg batter, and fried as one piece.
Two slices of bread are sandwiched around a sweet (jam) or savory (ham and cheese) filling, dipped in an egg-and-milk batter, then pan-fried until golden and crisp on both sides. Salzburg market stalls and street bakeries sell them warm, dusted with sugar for the sweet version.