In a heavy saucepan over low heat, cook marshmallows, butter and peanut butter until marshmallows are melted; stir until blended. Remove from the heat; stir in chow mein noodles. Divide into 12 mounds on a waxed paper-lined pan.
With lightly buttered hands, quickly shape each mound into a nest; make an indentation in the center. Fill nests with jelly beans. Trim 1/2 in. from each cupcake liner; place nests in liners. Store in an airtight container.