Prep the pan
Grease a 9×13-inch baking dish with butter or non-stick spray. Set aside.

Melt the base
In a large pot over medium heat, melt the butter. Once melted, add the marshmallows and stir continuously until completely melted and smooth.

Add cocoa & vanilla
Stir in the cocoa powder until well blended. Then add vanilla extract if using.

Mix in the cereal
Remove from heat. Quickly stir in the Rice Krispies cereal until evenly coated.

Add the chocolate chips
Let the mixture cool for about 1 minute, then stir in the chocolate chips (this keeps them from fully melting—so you get chunks). Save a few chips to press into the top if you like.

Press into pan
Gently press the mixture into the prepared pan. Don’t compact it too tightly—it helps keep them soft.

Cool and slice
Let cool at room temperature for about 30–60 minutes, then cut into squares.

Optional Add-Ins:

A drizzle of melted white chocolate on top

Sprinkle with sea salt

Use chocolate-flavored Rice Krispies for extra chocolate punch