Ristretto is espresso made by firmly packing enough espresso beans for a double shot, and only pulling a single, while cutting the process before it turns blonde (before the cream comes out). It is hailed as the most delicious part of the espresso because it avoids the burnt taste that happens when the beans have more water pushed through them. Also, that first bit of coffee has most of the of oils from the beans in it, and the oils are where most of the aromas are found; ergo, you capture the essence of the espresso in the ristretto more than you would in a normal shot which is "watered down" with the "ass end" of the drink.