Add butter to large stock pot on stove top
Using medium heat, melt butter
Once butter is melted, add bag of marshmallows
Stir marshmallows until completely melted
Remove marshmallow/butter mixture from heat
Pour in Fruit Loops
Stir until cereal and marshmallow/butter are thoroughly mixed
Pour mixture into 9x13 brownie pan
Using a spatula, pat down mixture until it is evenly spread throughout the pan
Allow treats to cool
Cut, serve, and enjoy!