For a sweeter sling, increase the amount of simple syrup to 0.75 ounce. For a drier sling, reduce it to 0.25 ounce or omit it entirely. Feel free to experiment with different types of gin and bitters to customize the flavor profile to your preference. Orange bitters can be a great alternative to Angostura. If you don't have simple syrup on hand, you can make it easily by combining equal parts sugar and water in a saucepan. Heat over medium heat, stirring until the sugar dissolves completely. Let cool before using. The lemon peel garnish is important. Twist it over the drink to release the oils.