Combine ¼ cup water and ½ cup sugar in a medium saucepan over medium-high heat. Stir until the sugar dissolves, about 5 minutes. (Avoid low heat, which can dry out the sugar.)
Cover the pot while it boils, about 3 minutes. Remove the lid and continue stirring until the mixture turns a light amber color.
As soon as the color changes, remove the pan from heat. Let it cool slightly, about 1 minute.
Slowly pour in the remaining ¼ cup warm water, stirring constantly to prevent the sugar from seizing. Then stir in the vanilla extract, if using.
Once the syrup has cooled (warm to the touch is okay), stir 1 ounce and 1 pinch of salt into 7 ounces whiskey. Taste and add more syrup and salt if desired.
Notes
Cooking tip: When you heat the sugar and water together, low heat will dry out the sugar so make sure the heat is set to medium-high.Adjusting the sweetness: How sweet and flavorful you’d like the whiskey depends on your taste, so add the syrup in small amounts. Taste it with a spoon after each addition and add more if desired. You will need approximately ½ to 1 ounce for every 3 ounces of whiskey.Variations:
Caramel whiskey: Skip the salt to make an unsalted, sweeter caramel whiskey.
Salted caramel vodka: Use vodka instead of whiskey. Great for fall drinks!