3.5 ounces good quality bittersweet or semisweet chocolate, chopped (chocolate chips are fine)
1/2 cup heavy cream
1 teaspoon light corn syrup (optional)
1 teaspoon pure vanilla extract
Microwave the chocolate until melted. (microwave in 1 minute increments and stir between - the chocolate won't look melted until you stir it, and it is easy to burn if you heat for more than 1 minute at a a time) Pour the cream over the chocolate and stir using a small rubber spatula or whisk, starting from the center of the bowl and working your way out till combined and smooth. Add the corn syrup (if using) and vanilla. Stir into the chocolate mixture well. Using a hand mixer, beat the chocolate mixture for 2-3 minutes until it becomes softer and light and fluffy.
You can also just allow the chocolate mixture to cool for a few minutes and then pour it over the cake as a glaze.