Make sandwich as usual, with sliced untoasted bread. Heat frying pan and butter very liberally. When hot, put sandwich in pan and cover with lid. Flip when brown. Do not burn butter.
The result is crisp buttery bread on the outside and nice warm sandwich in the middle. Pure yum. This is the deluxe conclusion of something I've been doing a long time - when you make a sandwich and toast the bread, butter the bread on the *outside* not on the inside. Butter on the outside means you taste it more when you eat the sandwich because it's the first thing to hit your tongue. This works great for hamburger buns too. There's no need to put butter on the inside, the filling is moist enough, but a nice coat of the butter on the outside enhances the flavor and texture of the initial attack of the bun.