Best Grilled Cheese Sandwich I Make

This has been a favorite of mine since I was young and my mother made them for me. For this one you need:
Bread of your choosing
Sliced Roast Beef
Sliced Swiss Cheese
Butter
Olive Oil
Sliced Onion
Sliced Mushroom

In spite the fact that it's tasty and so simple to make, I've never encountered anyone else that makes a grilled cheese sandwich this way.