Creating Marshmallow Cocoa Puff Brownies is straightforward if you follow these simple steps:

1. Preheat the Oven: Start by preheating your oven to 350°F (175°C). Grease a 9×13-inch baking pan with butter or cooking spray.
2. Melt the Butter: In a medium saucepan over low heat, melt the butter completely. Remove from heat and let it cool slightly.
3. Mix Sugar and Eggs: In a large bowl, combine the melted butter and granulated sugar. Stir until well mixed. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
4. Combine Dry Ingredients: In another bowl, sift together the flour, cocoa powder, baking powder, and salt.
5. Incorporate Dry Ingredients: Gradually add the dry mixture to the wet mixture, stirring until just combined. Avoid overmixing.
6. Add Cocoa Puffs: Gently fold in the Cocoa Puffs cereal until evenly distributed throughout the batter.
7. Bake the Brownies: Pour the brownie batter into the prepared baking pan and spread it evenly. Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
8. Add Marshmallows: Remove the brownies from the oven and immediately sprinkle the mini marshmallows evenly over the top. Return to the oven and bake for an additional 5 minutes or until the marshmallows are puffed and slightly golden.
9. Cool: Allow the brownies to cool in the pan for about 15-20 minutes before slicing them into squares.

These steps will guide you in creating these incredible brownies effortlessly, ensuring a delicious treat that everyone will love.