From Whiskey in a Teacup by Reese Witherspoon
for the simple syrup
1 cup sugar
1 cup distilled water
for the mint julep
2 bunches fresh spearmint
4 cups bourbon
powdered sugar for garnish
To make the simple syrup: Mix the sugar and water in a small saucepan. Heat to dissolve the sugar. Stir constantly so the sugar does not burn. Set aside to cool.
To make the mint extract: Wash about 40 small or 20 big mint leaves. Place in a small bowl. Cover with 3 ounces bourbon. Soak for 15 minutes. Then gather the leaves in paper towels. Wring the mint over the bowl of bourbon. Repeat the process several times.
To make the mint julep: Pour 3 1/2 cups of bourbon into a large glass bowl or glass pitcher. Add 1 cup of simple syrup to the bourbon. Now add the mint extract 1 tablespoon at a time to the mixture until it tastes as you'd like it to (3 tablespoons is usually about right). Pour the whole mixture back into a bottle or pitcher and refrigerate it for at least 24 hours.
To serve the julep, fill each glass (ideally a silver mint julep cup) half full with shaved ice. Insert a spring of mint and then more ice until the ice sits about 1 inch above the top of the cup). Pour the refrigerated julep mixture over the ice. Add a sprinkle of powdered sugar to the top of the ice.