Prep. Line a metal 8x8 or 9x9 square pan with parchment paper or lightly grease and set aside. Measure and gather all your ingredients and have them close by, since you'll need to work quickly once you get started.
Melt. In a large pot or Dutch oven, melt butter over medium-low heat. Add mini marshmallows and cocoa powder to the melted butter, and stir constantly until the marshmallows are melted and the melted marshmallow mixture is evenly blended.
Combine. Add chocolate chips, vanilla, and salt, and stir over low heat until the chocolate chips are just melted and the chocolate mixture is smooth.
Add Crisp Rice Cereal and stir until the cereal is evenly coated.
Gently Pat & Garnish. Transfer the cereal mixture to your prepared pan and use gentle pressure to lightly pat down the cereal into an even layer. You want it to stick together, but don't want to overly compact the cereal or the bars won't have that soft, gooey texture we're looking for. Sprinkle with mini chocolate chips, if using and gently pat down on them to lightly press them into the cereal layer.
Cool & Slice. Let the chocolate rice krispie treats cool to room temperature before slicing cereal bars into 9 large squares, 12 medium rectangles, or 16 small squares.
Serve & Store. Enjoy right away or store chocolate rice krispie squares in an airtight container up to 2-3 days at room temperature. (These treats are best enjoyed within 24 hours, but will still be good on day 2 & 3!)