Step 1: Grease a 9x13-inch baking pan with butter or non-stick cooking spray, or line with parchment paper, leaving an overhang on the sides for easy removal.
Step 2: In a large pot or Dutch oven, melt the unsalted butter over low heat. Ensure the butter melts slowly without browning.
Step 3: Add the mini marshmallows to the melted butter. Stir constantly over low heat until the marshmallows are completely melted and smooth. This usually takes about 3-5 minutes.
Step 4: Remove the pot from the heat. Stir in the vanilla extract and the pinch of salt until well combined.
Step 5: Add the Rice Krispies cereal to the marshmallow mixture. Using a buttered spatula or spoon, gently fold the cereal into the melted marshmallows until it is evenly coated. Be careful not to crush the cereal.
Step 6: Transfer the mixture immediately to your prepared 9x13-inch pan.
Step 7: Lightly butter your hands or a piece of parchment paper and gently press the mixture evenly into the pan. Do not press too firmly, as this can make the treats dense and hard.
Step 8: Allow the rice krispie treats to cool completely at room temperature for at least 30-60 minutes before cutting. This allows them to set properly and maintain their shape.
Step 9: Once cooled, use the parchment paper overhang to lift the entire slab of treats out of the pan. Place it on a cutting board and cut into 24 squares using a buttered knife. Serve and enjoy!