For the brown sugar simple syrup:Add brown sugar, vanilla extract, and ¼ cup water to a small saucepan. Place over medium heat and stir until sugar is fully dissolved. Allow to cool, then pour into a glass jar and seal tightly.
For the cocktail:Add Irish cream, peanut butter whiskey, vodka, 1 ounce brown sugar simple syrup, cream of coconut, and orange bitters to a cocktail shaker. Shake vigorously for 30 seconds. Strain into the prepared glass.