Spray a 9×13-inch pan with cooking spray, grease with butter, or line with parchment paper. Set aside.

Melt the butter in a large saucepan over low-medium heat. Add the marshmallows and salt. Stir continuously until fully melted and smooth.

Stir in the peanut butter and vanilla until smooth.

Remove from heat. Add the Rice Krispies cereal and stir quickly to combine before the mixture cools.

Transfer to the prepared pan. Use a buttered spatula to press the mixture into an even layer.

Melt the chocolate chips in the microwave on half power, stirring every 15 to 20 seconds, until smooth.

Pour the melted chocolate over the treats and spread into an even layer with a spatula.

Let the chocolate set completely before cutting into bars. This takes about one hour at room temperature. To speed things up, refrigerate the treats, then let them sit out for 10 minutes before cutting so the chocolate doesn't crack.