In medium glass bowl, combine chocolate and heavy cream. Microwave on high (100% power) for 30 seconds. Stir; microwave an additional 30 seconds, then stir until smooth.
Add corn syrup, peanut butter and vanilla. Stir until smooth. Microwave an additional minute on high (100% power), or until heated through. Serve immediately or refrigerate, tightly covered, for up to 1 month; heat briefly before serving. Makes 1-1/3 cups.
If preparing this with children, let them measure out ingredients and stir after microwaving, using oven mitts to hold the bowl or cup.