In a small bowl, heat the chocolate chips in the microwave (at 50% power) until almost melted. Stir until fully melted and smooth, then set aside.
In the bowl of an electric mixer (using the paddle attachment), blend (room temperature) cream cheese until fully smooth.
Add sugar and salt and blend. Add sour cream and vanilla and continue to blend.
Add melted (and cooled) chocolate and blend to combine.
Crack the egg into a small bowl and beat with a fork, then add egg to the cheesecake mixture and blend on low speed until just combined.
Do not beat the mixture too much after the egg is added or you will incorporate too much air - causing it to later puff up and deflate.
Pour filling into baked crusts.
Prepare a water bath for the cheesecakes (as pictured) by wrapping the outside of the cheesecake pans with foil, then set in a baking pan (such as a 9"x9" pan). Pour hot water into the larger pan until the water comes to about halfway up the outsides of the cheesecake pans.
Bake at 300°F for about 45 minutes, or until the edges are set and the center is just slightly jiggly but not wet.
Turn off oven and crack the oven door, but leave cheesecakes inside oven for an additional 5-10 minutes.
Remove cheesecakes from oven and continue to cool at room temperature for 30 minutes.
Once cooled to room temperature, cover cheesecakes and move to the fridge. Chill for at least 4 hours, or overnight.
Once the cheesecake is fully chilled, prepare chocolate topping.
Add chocolate chips to a small bowl and set aside.
Heat heavy cream until hot (but do not boil), and pour hot cream over chocolate chips. Allow to sit 1 minute, then stir until the chocolate chips are melted and cream and chocolate is fully combined.
While the chocolate cools slightly, remove cheesecake from fridge and carefully remove outer ring of springform pan. For best results, before loosening the lock on the outer ring, heat a small off-set spatula with hot water, then dry off and run the spatula along the inside ring of the pan to loosen cheesecake. Then unlock the outer ring and remove. If desired, remove cheesecake from the base as well and place on a plate.
Spoon chocolate topping onto the center of each cheesecake, spreading to almost the edge, as desired.
Return cheesecakes to the fridge and chill at least 30 minutes to allow the topping to firm up.
Remove cheesecakes from the fridge just before serving. Slice with a sharp knife that has been run under hot water and then dried off.