Spread the pieces of French bread in the prepared dish and drizzle with butter. Sprinkle with sausage, Swiss, and cheddar cheeses. In a large bowl, whisk the eggs, milk, wine, green onions, mustard and pepper. Beat until foamy. Pour over the casserole, cover with plastic wrap and refrigerate overnight. If you want-- you can place a book on top of the plastic wrap to weight down the ingredients.
Remove the casserole from the refrigerator 30 minutes before baking. Preheat the oven to 325 degrees. Remove the plastic wrap, then cover with foil and bake for one hour.
Remove the casserole from the oven. Spread with the sour cream and sprinkle with Parmesan. Bake, uncovered, for an additional 10 minutes, or until lightly browned.