In a small bowl, combine the mayonnaise, salad dressing and Dijon mustard; spread over 1 side of each slice of bread. On 4 slices, layer the turkey, ham and Swiss cheese; top with remaining bread. In a shallow bowl, combine the eggs, cream and ground mustard. Dip sandwiches in egg mixture.
Using a large cast-iron skillet or electric griddle melt butter; toast sandwiches over medium heat until bread is golden brown, 2-3 minutes on each side. Serve with preserves.