Prepare your pan. For thick bars: Grease an 8x8x2-inch pan with nonstick cooking spray or softened butter. For thin bars: grease a 9x13 inch pan with nonstick cooking spray or butter.
For the easiest removal, line the pan with two pieces of crisscrossed parchment paper.
Melt the butter. In a large pot, melt the butter over low heat. You don’t want it to sizzle.
Add the marshmallows. Add the marshmallows and stir to combine. Continue stirring until marshmallows are melted. To keep the krispie treats soft and not crunchy, melt the marshmallows slowly over low heat.
Add the cereal. Remove the pot from the heat and stir in the cereal until coated.
Press into pan. Place the mixture into the prepared pan and gently press into place. A greased metal spatula makes this easy.
Cut into squares. Allow the bars to set for an hour or so and then cut into bars.
Store at room temperature. Rice Krispie treats are best enjoyed the day they are made. However, you can cover the leftovers and store at room temperature.
Butter: Use salted or unsalted butter. An equal amount of coconut oil or margarine may also be used.
Marshmallows: Mini-marshamallows melt the easiest. Avoid "jumbo" marshmallows (These are sometimes called s'more marshmallows) The jumbo marshmallows take a long time to melt and can make for hard rice krispie bars.
Store: Cover the bars and store on the counter. Rice Krispie treats may be refrigerated or frozen. Place a piece of waxed paper between the bars before chilling. For the best texture allow the bars to come to room temperature before serving.