Melt the chocolate chips with the heavy cream over a double boiler or in the microwave in 20-second bursts, stirring until smooth. Stir in the Godiva chocolate liqueur and set aside to cool until barely warm.

Beat the softened cream cheese and sugar on medium-low until smooth. Add the eggs one at a time, mixing just until each disappears. Blend in the sour cream, vanilla, sifted cocoa powder, flour, and salt, then mix in the cooled chocolate until evenly colored.

Pour the filling over the frozen crust, smooth the top, and rap the pan on the counter to release air bubbles. Bake at 325°F for 60 to 70 minutes, until the edges are set and the center two inches still wobble as one piece.

Turn the oven off, prop the door open, and leave the cheesecake inside for 1 hour. Run a knife around the inside edge of the pan, then refrigerate uncovered for at least 6 hours or overnight.

Pour steaming heavy cream over the chopped chocolate, wait two minutes, then stir from the center outward until glossy. Stir in the liqueur if using.

Cool the ganache until barely warm, pour it over the chilled cheesecake, and tilt to spread. Chill 20 minutes before slicing with a hot, dry knife.