Combine the first 4 ingredients and place in a 9' x 11 " baking dish. Bake at 300 degrees for 30 minutes. Remove from oven and add brown sugar, stirring until mixed.

Remove half of the cereal mixture. With the remaining mixture spread across the bottom of the pan, spread the softened vanilla ice cream over the mixture. Pack firm. Top with the remaining cereal mix. Freeze until firm. Cut into squares to serve.