I was raised in Kentucky, and this is as close to the original recipe (from the Brown Hotel in Louisville) as I've ever tasted. You can substitute cheddar cheese if you like, but the swiss makes it more like the original dish.
Heat butter over medium heat. Add flour and whisk, slowly cooking for about 4-5 minutes. Whisk in cram and milk and continue to heat. Whisk in cheese, slowly, until melted. SEason with salt and pepper. Simmer for about half an hour (sauce will be thick).
Quarter the toast and place in 6" ramekins, or any oven-safe dish. Top with turkey and tomatoes. Cover with the sauce (be generous, it's good!). Bake at 400 degrees for 10 minutes or so.