Prep the pan. Lightly butter or spray an 8x8 or 9x9 pan. For easier removal, line it with parchment, leaving overhang on two sides.

Melt the butter. In a large pot over low heat, melt the butter gently. Don’t rush this step; low heat keeps the marshmallows from getting tough later.

Add most of the marshmallows. Stir in about 9 cups of the mini marshmallows, reserving 1 cup for later. Keep the heat on low and stir constantly until fully melted and smooth.

Optional flavor boost. If using unsalted butter, add a small pinch of salt now. It makes the sweetness pop without tasting salty.

Fold in cereal. Remove the pot from heat. Add the Rice Krispies and fold gently with a buttered spatula until everything is well coated.

Stir in the remaining marshmallows. Quickly fold in the last 1 cup of mini marshmallows for extra gooey pockets. Work fast so they soften but don’t fully melt.

Press into the pan. Transfer the mixture to your prepared pan. Lightly butter your hands or a spatula and press the mixture in gently. Don’t pack it down hard or the treats will be dense.

Let set, then slice. Allow to cool at room temperature for 30–45 minutes. Use the parchment to lift out, then cut into squares with a sharp knife.