Line a 9-inch square baking dish with parchment paper. Set aside.
In a large saucepan, melt butter over medium heat. Once melted, add in all but 1 cup of the marshmallows. Reduce heat to low and continue stirring until completely melted.
Remove from heat and stir in the vanilla. Add the chocolate cereal and the remaining 1 cup of marshmallows.
Pour into the prepared baking dish. Press GENTLY with your fingertips just until completely spread out (the harder you pack them in, the harder they are to eat).
Allow to set, about 1 hour. Cut and enjoy!
Notes
Press the mixture GENTLY into the pan. If you use a lot of pressure, the Chocolate Rice Krispie Treats will be hard instead of soft and chewy.
If you’re making football shapes, coat the cookie cutter with nonstick spray to keep it from getting sticky.
Save the butter wrapper! You can use it to press the Cocoa Krispie mixture into the pan. The residual butter on the wrapper will keep it from sticking and using the wrapper to press will keep your fingers from getting sticky.
Store Chocolate Rice krispie Treats in an airtight container or ziploc bag at room temperature for up to one week. Or freeze krispie treats for up to 3 onths.