Preheat oven to 350 degrees. Prepare a 9?x11? baking dish by spraying with non-stick cooking spray.
Cook shells according to package directions. Mix together all ingredients for filling. Divide filling between shells and arrange in prepared baking dish.
To make sauce, place butter in a large skillet over medium heat. When butter has melted, whisk in flour and continue to cook for about 1 minute.
Add half & half and white wine/chicken broth and whisk constantly until well blended.
Add onion then reduce heat to medium and simmer until thickened, about 3-5 minutes, stirring often.
Add Worcestershire sauce and shredded Swiss cheese and continue to stir until melted then add salt, pepper and sherry. If sauce is too thick you can add additional white wine/chicken broth.
Pour sauce over shells and top with Panko crumbs and grated Parmesan cheese.
Bake in oven for 30 minutes. Serve with side salad and a loaf of French bread.