Preheat oven to 250 degrees Fahrenheit (120 degrees Celsius).

In a large mixing bowl, combine Rice Chex and Corn Chex cereal.

In a microwave-safe bowl, melt the butter.

Whisk the sugar, ground cinnamon, vanilla extract, and salt into the melted butter until well combined.

Pour the butter mixture over the cereal and toss gently until every piece is evenly coated.

Spread the mixture onto a large rimmed baking sheet in a single layer.

Bake for 45 minutes, stirring every 15 minutes to ensure even drying.

Remove from oven and allow to cool completely on the baking sheet before serving or storing.