First, make your simple syrup. Place the sugar and water in a small pot, bring to a boil, and stir until the sugar has completely dissolved. Place the bunch of mint leaves in a heatproof bowl or container and pour the syrup over them. Allow the mint leaves to steep in the syrup for at least 1 hour in the fridge (you can let them steep for up to 24 hours). When you're ready, strain the mint leaves from the syrup, discard the leaves, and set the syrup aside.
Now, make your cocktail. Place 25 to 30 mint leaves in a cocktail shaker and muddle them well to release their oils and aromas. Pour in the 7 ounces of bourbon and 2 ounces of mint syrup, then top with a few ice cubes. Stir, don't shake, then strain the cocktail into two chilled, ice-filled glasses. Top each drink with a good amount of crushed ice (I made my crushed ice by putting regular cubes in a plastic bag, wrapping the bag in a paper towel, and bashing it with a rolling pin. It's basically therapy, after which you are rewarded with a delicious cocktail) and a small bunch of mint leaves.