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).
Harvest and wash four to six cups of mint plant tops. Use mostly leaves, although the 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. If you let it sit longer, the mint begins to rot and turn black and there’s an unpleasant mud flavor.
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.