Spray pam in 13x9 pan (save 1 cup marshamellow) In a large pan melt chocolate chips, butter, corn syrup and remaining marshamellows over low heat stir until Melted. Remove from heat...add Vanilla extract.

Pour cereal into sauce stir until coated with chocolate... Stir the rest of saved marshamellow into mixing bowl. Press into pan and cool at room temperature until firm about 1 hour.