Bake: Mix cake ingredients and bake in a greased 9×13 pan according to box instructions.
Poke: Immediately after removing from the oven, poke holes across the entire top using the end of a wooden spoon.
Make Soak: Microwave condensed milk and Hershey rectangles for 30 seconds, stir, then microwave 15 seconds more. Stir until smooth and combined.
Infuse: Pour the chocolate mixture over the cake, using a spatula to push it into the holes. Cool on the counter for 1 hour, then refrigerate for 2 hours to set.
Prep Bowl: Place a large mixing bowl in the freezer to chill for the topping.
Whip Cream: In the chilled bowl, beat heavy cream until thick. Add powdered sugar, cocoa, and vanilla; beat until stiff peaks form.
Decorate: Spread the whipped topping over the cold cake. Drizzle with syrup and sprinkle with mini chips.
Serve: Keep refrigerated until ready to serve.