Prep your pan: Lightly grease a 9x13-inch baking dish with butter or nonstick spray. You can also line it with parchment for easier removal.

Measure the cereal: Add the Rice Krispies to a large mixing bowl and set aside. This makes it easier and faster to combine when the marshmallow mixture is ready.

Melt the butter: In a large pot over low heat, melt the butter completely. Keep the heat low to prevent scorching.

Add peanut butter: Stir in the peanut butter until smooth and fully combined with the melted butter.

Melt the marshmallows: Add the marshmallows and salt to the pot. Stir constantly over low heat until the marshmallows are fully melted and glossy. If using vanilla, stir it in now. For extra gooey treats, reserve a small handful of marshmallows to fold in later.

Combine with cereal: Immediately pour the warm marshmallow mixture over the cereal. Use a spatula to gently fold until everything is evenly coated. If you reserved extra marshmallows, fold them in now for little pockets of gooeyness.

Press into the pan: Transfer the mixture to the prepared pan. Lightly grease your hands or a piece of parchment and gently press the mixture into an even layer. Don’t pack too firmly—light pressure keeps the treats soft and chewy.

Optional finish: Sprinkle chocolate chips on top while warm and let them soften, or drizzle melted chocolate over the cooled bars. A tiny pinch of flaky sea salt is great here too.

Let set and slice: Allow the treats to cool at room temperature for 30–45 minutes. Cut into squares with a sharp knife. For the cleanest cuts, lightly grease the knife.