In the container of a blender, add eggs, milk, and salt, and process until smooth. Lay 7 slices of bread on work surface, and place 1 slice each of Swiss cheese, ham, and turkey on each slice; top each with remaining 7 bread slices. Cut each sandwich into fourths. Place in prepared dish, cut side up. Pour egg mixture over sandwiches, and sprinkle with Gruyère cheese. Cover and refrigerate overnight. Let stand at room temperature for 30 minutes before baking.
Preheat oven to 375°.
Cover casserole with foil coated with cooking spray, and bake for 40 to 45 minutes. Remove foil, and bake until center of casserole is 160° and puffed, about 15 minutes more.
In a small bowl, combine marmalade and mustard. Serve casserole hot with marmalade mixture.
Notes
KITCHEN TIP To bake from frozen, follow instructions through step 6, and place biscuits in an airtight container or cover with plastic wrap, and place in freezer overnight. The next morning, preheat oven to 425°, and bake until tops are golden brown, 20 to 25 minutes.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/overnight-monte-cristo-casserole/