It helps if you grow mint in your yard. The best mint is the kind with a sharp flavor—peppermint of some kind. Spearmint is a no-no—your julep will taste like toothpaste. Wintergreen is just lame. And no, lemon balm is not a mint—now the julep tastes like Lemon Pledge! Use peppermint. I have three kinds in my yard—a native peppermint (sharp and clean), a cultivated peppermint (hardy, fresh, fairly strong), and a chocolate peppermint (supersharp with a chocolatey overtone).
Cut and wash four to six cups of mint plant tops. Use mostly leaves, although soft upper stems and a few flowers are okay. Throw this into a blender with half a cup of powdered sugar. (Regular sugar takes forever to dissolve.) Add an entire fifth of bourbon. About any brand will do, but personally I stay away from Jack, which I find harsh. Blend until the leaves are all shredded and the powdered sugar is dissolved.
Pour all this into a jar or a bowl and refrigerate it, covered, for an hour—no longer—and then strain out the shredded peppermint greens and discard them.
Stuff a few sprigs of mint (with flowers if you like) stem-first down into the empty bourbon bottle.
Pour the bourbon back into the bourbon bottle. Hint: It won’t all fit! You will be forced to drink some. Also, the juleps will be cloudy and you’ll have a few bits of shredded greens in the bottom. That’s the part you’ll have to drink.
Refrigerate for a day or so until it’s time to pour the juleps over crushed ice and serve.
By now, you know that a little julep goes a long way. Give your guests lots of crushed ice and only a little julep, unless you have plenty of couches where they can sleep it off.