Bake the croissants as the directions on the package state.
Once the croissants have cooled, preheat the oven to 350F and spray a 9x13 casserole dish with some nonstick cooking spray.
Cut open the 8 croissants then spread the mayonnaise evenly between all 8. Cut the deli ham and Swiss cheese into enough slices so that you have enough to divide evenly over the 8 croissants.
Cut each sandwich into 4 pieces then spread pieces out in the casserole dish covering all areas.
In a large measuring cup or bowl, whisk together the eggs, milk, and a dash of salt and pepper. Pour the egg mixture over the croissants, being sure to cover all areas.
Cover the casserole with tin foil and bake in the oven for 30 minutes. Then remove the foil and bake for another 10 minutes.
Remove the casserole from the oven and let it cool for 5 minutes then cut into 6 equal servings. Each serving will weigh approx 6oz.