Preheat oven to the temperature required for your brownie recipe. Lightly grease a 10" spring form pan
Prepare your favorite brownie batter recipe as directed.
Spread the batter in the bottom of the spring form pan.
Bake at the recommended temperature for 1/3 to 1/2 the recommended time - the brownies should be under-cooked.
Set aside to cool while preparing the cheesecake batter.
Preheat oven to 350°F
In a small microwave safe bowl melt together 1/4 cup coffee and 6 oz milk chocolate. Set aside.
In another small microwave safe bowl melt together 1/8 cup coffee and 4 oz bittersweet chocolate. Set aside.
In a large mixing bowl cream together the cream cheese and sugar.
Add the eggs one at a time, beating to combine after each addition.
Blend in the sour cream, corn starch and vanilla.
Slowly mix in the milk chocolate mixture just until combined.
Gently pour about 3/4 of the batter over the cooled brownie layer in the spring form pan and spread evenly. Set aside.
Mix the bittersweet chocolate mixture into the reserved 1/4 of the batter.
Put the remainder of the batter in a pastry bag fitted with a long slender tip.
Use the pastry bag to inject the bittersweet chocolate batter into the layer of batter already in the pan. Try to space the injections so they do not bleed into each other. This will create a polka dot effect in the finished sliced cheesecake. If you do not have a pastry bag or appropriate tip simply spoon the remainder of the batter over the top of the batter layer in the pan and use a knife to swirl it through.
Bake the cheesecake in the preheated oven for 15 minutes.
Reduce heat to 250° and continue to bake for approximately 60 minutes or until the edges are firm and the center is slightly wobbly.
Turn off the heat and leave the cake in the oven for an additional hour. Remove from the oven and allow it to cool completely then cover it and refrigerate until chilled (~4 hours)
In a microwave safe bowl combine all of the ingredients for the Dark Chocolate Mocha Ganache.
Heat on high in the microwave for 30 seconds. Let it stand for 2 minutes before attempting to stir. If the chocolate is still too firm, return to the microwave for up to 10 seconds at a time. The final mixture should be smooth and shiny.
Spread the ganache over the top of the chilled cheesecake. Return to the refrigerator to set.