In a medium saucepan over low heat, combine the butter and marshmallows. Stir constantly for about 5-7 minutes, until the mixture is smooth and glossy.

While your butter and marshmallow mixture cools slightly, whisk together the all-purpose flour, baking powder, salt, and brown sugar for about 1-2 minutes.

Once the marshmallow mix has cooled a bit, beat in the eggs and vanilla extract until well combined. Slowly fold the dry ingredients into this wet mixture.

Gently fold in the crispy rice cereal with your spatula, ensuring the cereal is evenly coated with the cookie dough.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Drop spoonfuls of the cookie dough onto the prepared sheet.

Bake for 10-12 minutes until the edges are golden. Allow cookies to cool on the baking sheet for about 5 minutes before transferring to a wire rack.