Place the cereals and nuts in a large microwavable bowl. In a separate bowl, microwave the brown sugar, butter, and corn syrup uncovered on high for 2 minutes, stirring once after 1 minute, until melted and smooth. Stir in the baking soda until dissolved.

Pour the liquid over the dry mixture and mix lightly until evenly coated. Microwave on high for 5-8 minutes, stirring and scraping the bowl after every minute, until cereal begins to brown.

Cool for 5 minutes. (Optional: Add the M&M’s now and mix:) Spread on wax paper and allow to cool until you can break into bite size pieces. Store in air tight container.