Ok, go to your liquor cabinet and pull out your bar guide, should you have one. Look under "p" - do you see pisco sour? If yes, you have a better bar guide than the ones I've been looking at. And you should reward yourself with a pisco sour.
If you google pisco sour, you will likely find several recipes: at least, Gwen and I did. And our pisco sour attempts were fun and tasty, but they did not taste like the drinks we sucked back in Chile. Thus, when Bernardo excused himself to spend some time with the blender, Gwen and I eagerly followed for a lesson.
Step 1 in the Bernardo Pisco Lesson: assemble ingredients: lemons (or, better yet, key limes), sugar (plain white refined sugar), pisco (if lacking pisco, substitute grappa, but tell no-one), eggs, and ice. Step 2: apply some pressures to the lemons as you roll them around, to make the juicing easier. Juice them. You need lots of lemon juice. Count the number of people who are hanging out in the kitchen, mutliply by three, and perhaps you will come close in the lemons required count...
Next step (I have already lost count of the step numbering): Take the pisco and put it in the blender. You need about the same volume of pisco as lemon juice. Before putting the pisco in the blender, though, make sure that the bottom seal is nice and tight, otherwise, the precious pisco may leak all over the counter and that would be a waste. Go and 
crush some ice. You can do this in the blender, but not if it's a not-so-strong plastic blender, because then, instead of pisco on the counter, you will have pisco throughout the kitchen. Bernardo has empirically verified this, just like we empirically verified the counter spillage. If no heavy duty blender, crush the ice to a fine snow-like consistency in someone's food processor. You need as much crushed ice as you have lemon juice.
Run the blender to mix the ice and pisco. Add the lemon juice. Blend. Then, start adding the sugar, a bit at a time. You want almost as much sugar, total, as you have lemon juice (by volume), but keep tasting. This part is fun. Gwen and I were very good at it. Finally, take an egg, knock a hole in its end, and dump the egg white (but not the yolk) into the blender. Blend till frothy. Start next batch, because by this time, the people in the kitchen will be pushing their glasses at you...
There, that's the pisco recipe: 1 part pisco, 1 part ice, 1 part lemon juice. Just less than 1 part sugar. I egg white (we used one for about 6 cups of pisco sour). If making a Peruvian pisco sour, you also need some bitters. If making pisco sour with a Chilean, you will need some more pisco, because after he pronounces it perfect and finished, he pours more pisco into the blender.