Arrange 4 slices of bread to face each other as you would while making a sandwich
Lightly butter the top side of each slice
Add thin slices of banana on one half and brown sugar & a sprinkle of cinnamon on the other and then sandwich together. OPTIONAL: If you are a fan of walnuts, add some crumbled walnuts over the banana slices before sandwiching together.
In a large bowl (make sure it's wide enough to fit the length of the slices) beat the two eggs with the milk & vanilla.
Dip each sandwich in the egg mixture until well coated on all sides and then place on the hot panini grill.