Line a 9×9-inch baking pan with parchment, leaving an overhang for easy lifting. Lightly grease the paper with nonstick spray or butter.

In a large pot over low-medium heat, melt butter until bubbling gently. Add marshmallows in batches, stirring constantly with a heat-proof spatula. Tip: low heat prevents scorching.

Once marshmallows are smooth, remove pot from heat and whisk in 3/4 cup peanut butter until fully combined. The mixture should look glossy and pull away from the sides of the pan.

Immediately add Rice Krispies, stirring briskly so each flake is coated evenly. Work quickly—the mixture sets fast. For extra texture, toss in a handful of chopped peanuts here.

Transfer mix to prepared pan. Using a piece of parchment or a lightly oiled spatula, press the cereal mixture down firmly but not so hard it becomes rock-solid.

In a microwave-safe bowl, heat chocolate chips and 2 tbsp peanut butter in 20-second bursts, stirring after each, until smooth. Drizzle over bars in thin, even lines. Sprinkle sea salt or festive sprinkles while chocolate is warm.

Refrigerate for at least 30 minutes, or until chocolate finish is set. Use a sharp knife warmed under hot water (then dried) to cut into 16–20 bars.