In a large Dutch oven or stockpot, combine the butter, corn syrup, and brown sugar. Stir to melt and combine until smooth. Continue to heat until it just begins to boil. Remove from heat.
Stir the baking soda, vanilla, and salt into the sauce.
Pour the cereals and cashews into the sauce, stirring to coat the cereal.
Place the pan directly into the oven to bake on 300° for 30 minutes, stirring the mix halfway through.
Pour out on parchment paper, breaking apart large pieces.