In a medium saucepan, whisk together all ingredients except vanilla. Bring to a boil over medium heat, then reduce heat to medium low, and simmer 10-15 minutes while gently smashing the apples against the pan with the back of a fork. Continue to simmer until mixture is reduced and coats the back of a spoon.
Turn off heat and let syrup cool completely. Strain though a fine-mesh sieve into a glass jar. Stir in vanilla extract. Store in refrigerator.
Note
Use Apple Brown Sugar Syrup in coffee drinks, on pancakes, drizzled over warm oatmeal, or any way you can think of!