1. For simple syrup, add sugar and water into a heavy bottom saucepan. Allow mixture to boil. Stir continuously.
2. Once sugar is fully dissolved, remove from heat and let mixture cool completely.
3. When cool, your simple syrup is ready to use. Store in an air-tight jar in refrigerator for up to one month.
4. To make Brown Sugar Manhattan, place 1-2 ice cubes into cocktail shaker. Add whiskey, vermouth, simple syrup, and bitters. Shake well to combine.
5. Strain mixture into a coupe glass. Garnish with cherry.