Line an 8-inch square pan with aluminum foil, leaving an overhang for lifting the bars out later; spray the foil with cooking spray and set the pan aside.

In a large microwave-safe bowl, combine 1 heaping cup creamy peanut butter, ½ cup light corn syrup, ½ cup granulated sugar, and ¼ cup packed light brown sugar. Microwave on high for 1 minute.

Stir the mixture (it may be granular). Return to the microwave and heat on high for 1 more minute. Stir until as smooth as possible; if still lumpy, microwave in additional 10–15 second bursts, stirring between bursts, until smooth.

Stir in 1 tablespoon vanilla extract and 3 tablespoons unsweetened natural cocoa powder until fully combined.

Add 3 cups Rice Krispies and stir until the cereal is evenly coated with the chocolate–peanut butter mixture.

Transfer the mixture to the prepared pan. Pack it down firmly and smooth the top with a spatula. Set the pan aside.

Crush or dice about 1 cup Butterfinger and set the pieces aside.

In a medium microwave-safe bowl, combine 1 cup semi-sweet chocolate chips and ¼ cup creamy peanut butter. Microwave on high for 1 minute, then stir. If the chips are not fully melted, microwave in 15-second bursts, stirring between each burst, until the mixture is smooth.

Pour the chocolate–peanut butter topping over the cereal base and spread lightly and evenly with a spatula.

While the topping is still warm, evenly sprinkle the crushed Butterfinger pieces over the top and press them in lightly so they adhere.

In the same medium bowl, place the remaining ¼ cup semi-sweet chocolate chips. Microwave on high for 1 minute, stir, then heat in 15-second bursts as needed until smooth. Using a spoon, drizzle this melted chocolate over the top of the bars.

Cover the pan with foil and refrigerate until completely set, at least 3 hours or overnight. For easier slicing, let the chilled bars sit at room temperature about 15 minutes before cutting.

Use the foil overhang to lift the bars from the pan and slice. Store airtight at room temperature up to 1 week, in the refrigerator up to 2 weeks, or in the freezer up to 6 months.