Line a 9x13 pan with foil all the way over the edges for easy removal, then grease with non-stick spray.
baking spray
Put the cinnamon cereal in a ziploc bag and use a rolling pin or other object to break up the cereal into chunky pieces, small, medium, and big.
3 cups cinnamon toast crunch cereal
In a large pot, melt the butter over medium heat. Continue cooking until the butter is foamy and a deep golden brown.
1 cup salted butter
Turn the heat to low and immediately add the marshmallows, vanilla, cinnamon and salt. Stir with a rubber spatula until the marshmallows are completely melted and smooth.
20 oz mini marshmallows, ¾ teaspoon vanilla, ½ teaspoon cinnamon, ½ teaspoon kosher salt
Add both cereals and stir until combined.
5 ½ cups rice krispies cereal
Pour the mixture into the prepared pan, then use the spatula to press gently until it’s roughly even across the pan. Be sure to press very gently for soft rice krispie treats.
Gently press in extra cereal pieces, if desired. Sprinkle w/ tiny bit of cinnamon to decorate, if desired.
Allow to cool to room temperature (or just dig in while they’re warm!), then cut and serve.