Start by placing the chopped bittersweet chocolate and the unsalted butter in a medium saucepan over low heat. Stir gently until both ingredients are completely melted and combined. This should take about 2-3 minutes.
Once the chocolate and butter are melted, add in the granulated sugar and unsweetened cocoa powder. Stir continuously until the mixture is smooth and glossy.
Gradually pour in the heavy whipping cream while whisking constantly. This will help to create a silky texture. Keep whisking until everything is combined and the sauce is heated through, about 2-3 more minutes.
Remove the saucepan from heat and stir in the vanilla extract. This adds a depth of flavor that enhances the chocolatey goodness.
Let the sauce cool for a few minutes before transferring it to a heat-proof container. Allow it to cool completely at room temperature before storing it in the refrigerator.
