In a large saucepan, cook the flour and butter together slowly for 2 minutes (do not allow the flour to color). Remove the pan from the heat and whisk in the boiling milk. Add the seasonings and boil the mixture, stirring constantly, for one minute. Reduce to a simmer and cook, stirring, until the mixture begins to thicken. Remove from the heat and stir in one cup of grated cheese. Place plastic wrap directly on the surface of the sauce and set aside.
In a small saucepan, melt the butter over low heat. Add the onion and cook just until translucent. Add the spinach and cook, stirring, over medium-high heat until the moisture evaporates. Stir 1/2 cup of the Mornay sauce (see recipe) into the spinach.
*We have occasionally taken a shortcut here and used frozen creamed spinach. If you chose this option, cook the spinach according to package directions, and do not add any Mornay sauce to the spinach.
Over low heat, combine the butter and oil in a large skillet. Add the onion and cook just until translucent. Add the chopped mushrooms and cook over medium-high heat until the moisture evaporates. Add the ham and heat through. Stir one cup of the Mornay sauce into the ham and mushroom mixture.
Preheat oven to 350°. Butter a 13 x 9 inch baking dish. Place two crepes in the bottom of the dish, side-by-side. Spread each crepe with a small amount of ham filling. Press a crepe on top of each stack and cover with a small amount of spinach filling. Repeat with alternating layers of crepes and filling, ending with a crepe. Pour the remaining Mornay sauce over the stacks. Sprinkle with the reserved Swiss cheese. Bake for 25-30 minutes or until bubbly and the top is lightly browned. To serve, cut into pie-shaped wedges.