Prep the pan. Lightly grease a 9x13-inch pan or line it with parchment, leaving some overhang for easy lifting. Set aside.

Melt the butter. In a large pot over low heat, melt the butter slowly. Keep the heat gentle to avoid scorching.

Add marshmallows. Stir in the mini marshmallows and cook on low, stirring constantly, until they’re almost fully melted and smooth. Take your time here for the best texture.

Flavor it. Remove the pot from the heat. Stir in the vanilla extract and salt until evenly combined.

Fold in the cereal. Add the Rice Krispies and use a spatula to fold gently until every piece is coated. Don’t crush the cereal—light, even strokes work best.

Press into the pan. Transfer the mixture to the prepared pan. Lightly grease your spatula or your hands, or use a piece of parchment to press the mixture into an even layer. Do not press too firmly or the bars will turn hard.

Set and slice. Let the treats cool at room temperature for 30–45 minutes. Cut into squares and serve.