not for beginners!
peanut butter
jelly
bread
Now for constructing the sandwich.. first you must toast some bread. Select three matching pieces with a minimum of large holes in them. Toast until medium firm. Then allow bread to return to room temperature. This is crucial in what is to follow.
Arrange your bread so that when stacked, the outlines match. When finished, the sandwich will be from the top down: bread, peanut butter, jelly, bread, jelly, peanut butter, bread. Both peanut butter and jelly should be well chilled (this increases their viscosity) and bread should be room temperature.
Begin by spreading generous amounts (ie a large knifeful) of peanut butter on each of the endpieces. Go all the way to the edges and make the surface concave. The idea is to have the peanut butter form a seal to hold a large amount of jelly in. This is why keeping the peanut butter cold is crucial. Now spread an equally large quantity of jelly (1.5-2 knifefuls) on the bottom of the middle piece of bread. Note that it should not go all the way to the edges or you will be unable to make your sandwich seal. Now assemble the bottom two layers, squeeze slightly to seal, and use the peanut butter knife (you are using two knives, right?) to even out the edges.
For the upper layer, first spread jelly on the top of the middle piece of bread, being careful not to use too much force lest you cause the bottom layer to gush jam. Then carefully seal the top layer as above.
Now eat!