Line a 9" x 9" square pan with parchment paper leaving an overhang on two opposite sides for easy removal. If you don’t have parchment, spray the pan with cooking spray.
In a large, thick-bottomed pot, combine 1 ½ cups (345 g) unsweetened peanut butter, ½ cup (170 g) pure maple syrup (or honey), ½ cup (14 g, 8 Tbsp) unsalted butter (or coconut oil), and 1/4 tsp sea salt. Heat over medium-low to medium, stirring frequently, until everything is melted and smooth, about 2–4 minutes. Do not boil.
Remove the pot from the heat and stir in 1 tsp pure vanilla extract, if using.
Add 4 cups (112 g) crispy rice cereal to the melted mixture. Gently fold and stir until the cereal is evenly coated.
Transfer the cereal mixture to the prepared pan. Press it into an even layer using a spatula or the bottom of a measuring cup (press firmly but not so hard that the mixture becomes too compacted).
In a microwave-safe bowl, combine 1 cup (170 g) chocolate chips, 1 cup (170 g) butterscotch chips, and 2 Tbsp (29 g) unsalted butter. Microwave in 20-second intervals, stirring well between intervals, until the mixture is completely melted and smooth (about 1.5–2.5 minutes total). Alternatively, melt over low heat in a double boiler, stirring until smooth.
Pour the melted chocolate/butterscotch mixture over the pressed cereal layer and spread it evenly with a spatula. If desired, sprinkle a small amount of sea salt on top.
Place the pan in the freezer for about 30 minutes, or in the refrigerator until the chocolate topping is fully set.
Remove the pan from the freezer or refrigerator. Use the parchment overhang to lift the whole slab onto a cutting board. Let sit 10–15 minutes at room temperature so the bars are easier to cut.
Use a sharp knife to cut into squares (recommended: 25 pieces) or your preferred size. Serve and enjoy.