Line a square baking dish with parchment paper to make handles. Lightly butter the dish and set aside.
Place the ¼ cup of butter and chocolate chips in a large microwave safe bowl. Melt in the microwave, about 1 to 2 minutes.
¼ cup butter, ½ cup chocolate chips or chunks
Add the cocoa and stir well. Add the marshmallows to the melted chocolate mixture and stir well to coat.
¼ cup cocoa powder, 40 large marshmallows
Place the bowl back in the microwave and heat the marshmallows until they are puffy and inflated, about 1 to 2 minutes.
Remove the bowl from the microwave and, using a wooden spoon or rubber spatula, stir the marshmallows.
If they are still holding their shape after stirring, continue to cook in 30 second bursts, stirring each time, until they are smooth and creamy.
Add the vanilla to the melted marshmallow mixture and stir well to combine.
1 tablespoon vanilla extract
Pour the Rice Krispies into the bowl. Stir well until all of the Rice Krispies are coated in melted chocolate and marshmallow and the marshmallow mixture is evenly distributed.
5 ½ cups Rice Krispies or other crispy rice cereal
Scrape the mixture into the prepared buttered pan. Use a small piece of parchment paper to gently press it evenly into the pan, including the corners.
Cool the Rice Krispie treats for at least 30 minutes before slicing.