In a medium saucepan combine sugar and evaporated milk. Bring to a rolling boil. Simmer for 8 minutes.
Remove pan from stove and stir in butter, chocolate chips and vanilla. Stir until combined. Cool before layering it in the ice cream.
**Note: The sauce will thicken as it cools. Keep in refrigerator for up to 2 weeks. Once refrigerated it will be solid so warm up in the microwave or place container in hot water to return it to a pourable/spoonable state.