1) In a small saucepan, combine together the instant coffee, brown sugar, water, butter and corn syrup.
2) Slowly heat the mixture, constantly stirring, to bring to a boil. Then cook for 3 more minutes, stirring all the time.
3) Take the pan off the heat and add the semisweet-chocolate pieces and vanilla. Stir well till the chocolate has melted and the sauce is smooth.
4) Serve warm. To reheat the sauce, put it on top of a double boiler over simmering water.