Preheat oven to 350 F. Line baking sheet with parchment paper and set aside.
Place butter in a heat safe bowl and microwave for 15 to 20 seconds until only very slightly melted. Allow to cool a few minutes before adding sugar.
Add both sugars and vanilla, and mix on medium high until light and fluffy. About 2 to 3 minutes.
1 cup unsalted butter, room temperature, ¾ cup sugar, ¼ cup light brown sugar, packed, 1 tsp vanilla extract
Add egg and mix on medium low until fully incorporated.
1 ea large egg
Add dry cereal only to blender or food processor, and grind down to a fine powder.
In a separate bowl, combine flour, cereal powder, baking soda, baking powder and fine sea salt. Add to wet ingredients.
1 ¾ cup all purpose flour, 1 ¼ cup dry cereal only, ½ tsp baking powder, ¼ tsp baking soda, ½ tsp fine sea salt
Using a spatula, gently fold in the ingredients until fully combined.
Add marshmallows and gently fold in. Careful not to break or smash them.
1 ½ cup marshmallows
Using a 2 tbsp ice cream/cookie scoop, scoop out dough and roll in powdered dry cereal for coating. Top with extra cereal marshmallows.
Place on baking sheet at least 2" apart.
Bake for 9 - 10 minutes, or until you see a bit of browning along the bottom edges. The cookies will bake slightly underdone.
Remove from oven and place on cooling rack.
Using a large circle cookie cutter, or other large circular object (mason jar, bowl), scoot cookie to obtain round shape. Let cookies cool before enjoying.