Preheat oven to 350º F and lightly grease a 9×13-inch baking dish with butter or non-stick spray.
Mix cake mix with 1/2 cup (1 stick) melted butter, 1 egg and 1 teaspoon vanilla extract in a large bowl until just combined, then transfer to greased baking dish. Use a rubber spatula to spread the mixture into an even layer.
In a separate bowl or mixer, beat cream cheese for 2-3 minutes, or until smooth, then add eggs one at a time, waiting for each to be incorporated before adding the next. Mix in cocoa powder and instant coffee granules until smooth.
Gradually mix in powdered sugar (on low speed, if using a mixer), then drizzle in remaining melted butter and vanilla extract.
If using, fold in chocolate chips until just combined.
Pour mixture over batter into the baking dish and gently spread it into an even layer.
Place baking dish in oven and bake for 45-50 minutes, or until edges are pulling away from the sides of baking dish and the center is just set.
Remove from oven and let cool at least 40 minutes, or until set.
Slice, serve and enjoy!
