Combine all ingredients together in a medium saucepan over medium heat.
Heat, whisking frequently, until the peanut butter chips melt and all of the ingredients come together in a smooth sauce. It will be very thin at first.
As the sauce cools to room temperature, it will thicken up. If it gets too thick, simply return it to the heat and whisk until it loosens up. To store, pour it into a bowl or airtight container and press a layer of plastic wrap on top. Keep the peanut butter sauce in the refrigerator.
To reheat after chilling, gently microwave it in 20-second increments until warm and flowing. If it has separated, continue to whisk until it comes back together.