Place the brown sugar, water and the mint leaves in a pan over medium heat. Stir until the sugar is completely dissolved. Bring it to boil. Then lower the heat and let is simmer for 10 minutes. Move aside and let it cool for at least 2 hours.
Place all the ingredient for the cocktail plus two ice cubes in a shaker. Shake for a minute and pour in a glass dipped into brown sugar and filled with two ice cubes. Garnish with mint leaves.