Preheat and prep: Heat oven to 350°F (175°C). Grease a 9x13-inch baking pan and line with parchment for easy lifting.
Layer the add-ins: If using coconut and pecans, scatter them evenly over the bottom of the pan. This creates a toasty, candy-bar-like base.
Mix the cake batter: Prepare the chocolate cake mix according to the box directions.
Pour the batter over the coconut and pecans, smoothing the top.
Make the cream cheese mixture: In a bowl, beat softened cream cheese until smooth. Add melted butter, powdered sugar, vanilla, and a pinch of salt. Beat until thick and glossy.
Marble the top: Dollop spoonfuls of the cream cheese mixture over the cake batter.
Use a butter knife to swirl lightly. Don’t overmix—the dramatic streaks are the goal.
Add chocolate chips: Sprinkle over the top. They’ll sink in slightly and melt into pockets of fudgy goodness.
Bake: Bake 35–40 minutes, until the edges are set and the center still has a slight jiggle. Do not overbake. The middle should be gooey.
Cool and serve: Let the cake cool at least 20–30 minutes to set.
Slice warm for extra gooeyness, or cool completely for cleaner cuts.