Chunky, solid white bread, 2 Slices. (It's important that the bread is pretty solid).
Proper butter (none of this margerine nonsence).
Peanut Butter (chunky for preferance).
And, if you're being posh, a plate.
Spread each slice of bread with the butter. Then spread one slice with a thick, even layer of Marmite. Follow this by spreading the other slice with a thick layer of Peanut-butter.
Stick one slice to the other, toppings inward.
If you're being posh, place it on the plate.
It is recomended you accompany this treat with a large mug of strong, white tea. (See other guide entries on the subject - there must be hundreds).