In shallow dish combine eggs, Yogurt and salt. Brush Butter on one side of all eight pieces of bread.
Place one slice of ham, Swiss and Cheddar cheeses on the buttered side of 4 slices of bread. Top with remaining bread slices, buttered sides facing inward. Melt 2 tablespoons of butter in a heavy skillet over medium heat.
Holding sides of sandwiches, carefully dip in egg mixture and place in heated skillet. Cook until both sides are golden brown and cheese is melted, 3 to 4 minutes
per side. Add additional butter as necessary. Dust with powdered sugar; serve immediately.
Source: Wisconsin Milk Marketing Board