Line a 9x13 pan with foil and lightly grease with cooking spray.
To make the crust layer: Mix together 1 egg, ½ melted butter and cake mix. Press in an even layer into prepared pan. Bake for 15 minutes.
To make the gooey layer: Beat cream cheese until smooth. Add eggs, one at a time and beat until completely combined.
Add powdered sugar, about 1 cup at a time, mixing on low until well combined.
Pour in ½ cup melted butter, hot fudge, coffee and vanilla extract. Mix to combine and pour evenly over baked crust.
Return to the oven for 35 minutes (rotating the pan half way to ensure even cooking). The center won't be completely set, cool completely on a wire rack before cutting into bars.