Combine the half-and-half, butter, and corn syrup in a small, heavy saucepan over medium heat. Cook, stirring, until a thin paperlike skin appears on the top. Do not boil. Add the chocolate chips and vanilla and stir until the mixture is smooth. Remove from the heat and let cool.
The sauce can be refrigerated in an airtight container for several days, but it must be returned to room temperature before using.
Yield: 1 1/2 cups