It's all about the 'mallows.
Growing up, Rice Krispies squares were the treat most often found in our cupboard. Because they are (usually) gluten-free and easy to make, we'd spend some time on a Saturday with Mom in the kitchen melting the butter, counting out the marshmallows, and stirring in the cereal. One thing I distinctly remember, however, is how hard the squares were. We put in six cups of cereal – I remember this clearly, as that was my job – and stirred until the puffs were just barely coated. When we pressed into the pan and allowed to cool, the Rice Krispies squares were so tough (due to their ratio of cereal to marshmallow) that you could actually break them in half.
As an adult who loves to bake, I've only recently realized that Rice Krispies squares do not, in fact, need to be hard enough to chip your teeth. On the contrary: My favorite Rice Krispies squares are the ones that are a little too gooey and leave chunks of marshmallow on your hands. After experimenting with a few different recipes and sampling more-than-a-few Rice Krispies treats, I finally figured out the key to making those perfectly chewy squares.
For context, the original Rice Krispies brand recipe calls for 3 tablespoons of butter, one 10-oz. pack of regular marshmallows, and 6 cups of Rice Krispies cereal. We also used to throw in a teaspoon of vanilla, for a little extra flavor. In my current recipe, I've cut the 6 cups of cereal down to 4 or 5 cups (which will give you more like an 8 x 8 pan of bars instead of a 13 x 9), bumped the butter up to 1/4 cup, and embraced the mighty power of mini marshmallows.
Here's your trick: Instead of melting all of the marshmallows into the butter as the original recipe calls for, only melt 2/3 of the mini marshmallows. Once you have your butter-marshmallow mixture smooth and ready to go, remove from the heat and stir in a teaspoon of vanilla and the cereal. Coat the cereal in the mixture, and then stir in the remaining whole 1/3 package of mini marshmallows. The whole marshmallows will begin to melt a little when they hit the hot cereal, but they will remain mostly intact; the end result being pockets of marshmallow chunks that I've yet to find someone complain about.
You may also be interested in Cookies and Cream Crispy Treats:
These Rice Krispies squares are the best ones around. They remain soft even after a few days of being stored, and are hearty enough to hold together once cooled. And, don't get me started on the warm, gooey "batter." Once you start reserving some of your marshmallows to stir in later – you'll never go back!