Mix together cocoa, salt, and ⅔ cup of sugar. Mix until there are no more clumps, and then add in the cream cheese and sugar. Whip all of that together until smooth.
Next, mix in your eggs, one at a time. Then, add in vanilla and melted chocolate. Mix until smooth and then add sour cream and heavy cream and mix that all together as well.
You will likely have some air bubbles trapped in your mixture that you need to get rid of. To remove them, you will need to tap the bowl onto the countertop hard,30 times or so. Next, scoop out about ¼ of a cup of mixture into each muffin cup, over the crust.
Bake your black forest cupcakes for 17 minutes in an oven preheated to 325 degrees Fahrenheit. They are done when the center jiggles just slightly. Take them out of the oven and allow them to cool for about an hour, then cover them and refrigerate.