Combine the peanut butter and coconut oil in a small glass bowl or glass measuring cup. Microwave for 1 minute. Stir until combined. Add vanilla, if desired.
Allow the sauce to cool to room temperature before pouring it over ice cream. (It can be poured while warm, but it will be much thinner and won't create the same magic shell effect.) Store at room temperature and reheat for just a few seconds when needed, if it firms up too much to pour.
Notes
This peanut butter ice cream topping can also be made with creamy peanut butter. If you choose to use creamy peanut butter, reduce the amount of coconut oil by 1 tablespoon.For ZERO coconut flavor, use a refined coconut oil. If you don't mind, or prefer a hint of coconut flavor, use an unrefined coconut oil.