In a greased roasting pan, combine the popcorn, cereals and nuts. In a saucepan, bring the brown sugar, butter and corn syrup to a boil. Boil until a candy thermometer reads 250 (hard boil stage), about 5 minutes.
Remove from heat; immediately stir in vanilla and baking soda. Drizzle over popcorn mixture; toss to coat. Transfer to a greased 15-in. x 10-in. baking pan. Bake uncovered at 250 for 1 hour, stirring every 15 minutes. Yield: 3
Editor's Note: We recommend that you test your candy thermometer before each use by bringing water to a boil; the thermometer should read 212 degrees. Adjust your recipe temperature up or down based on your test.