Grease an 8"x 8" baking dish with butter or nonstick cooking spray.
In large pan slowly melt the butter. Don't let the butter bubble and burn.
Stir the marshmallows into the melted butter. Stir gently just until the marshmallows start to melt. Remove pot off the heat before completely melted and bubbling.
Stir in the Fruity Pebbles cereal and mix until combined.
Add in the additional 1/2 cup mini marshmallows and stir again until incorporated.
Press mixture into prepared baking dish and let set for about one hour.
Cut into squares and serve.
Notes
Mini marshmallows are used in this recipe. You can use the same amount in larger marshmallows but you will not get the whole marshmallow effect when we add in the 1/2 cup of mini marshmallows towards the end.
I use an 8"x 8" pan for these so they are thicker. If you want a thinner bar then you can use a 9"x 13" pan instead.
I like to add the extra mini marshmallows into the mixture so you get bursts of marshmallow goodness in each bar. I think it really makes it stand out when you cut into them too.
These need to set up for at least 1 hour before cutting into.
If you are not a fan of Fruity Pebbles then you should try Cocoa Pebbles for a chocolate version! However, this same recipe will also work with regular Rice Krispies too!