You'll need:

1/4 cup butter or margarine
1, 10oz. bag of mini marshmallows
6 cups of rice cereal (as an alternative use the crispy chow mein crunchy "noodles" that come out of the can)

Melt butter in microwave in large glass mixing bowl.  Remove carefully and stir in marshmallows saucepan over medium heat.   Continue heating in microwave until marshmallows have melted completely (be careful not to overcook).   Carefully stir in cereal or "noodle" crunchies and coat thoroughly. 

When mixture is cool enough to touch, remove small portions to wax paper and shape each into a "nest".    Let cool and add jelly beans into the nest.

For a fun variation, add chocolate chips in with the margarine, then add marshmallows.