Line an 8-inch square pan with aluminum foil leaving overhang, spray with cooking spray; set aside.

In a large microwave-safe bowl, combine 1 heaping cup peanut butter, corn syrup, sugars, and heat on high power for 1 minute to melt.

Stop to stir. Mixture will be on the granular side, this is okay.

Return bowl to microwave and heat for 1 more minute on high power.

Stir in the vanilla.

Stir in the cereal.

Turn mixture out into prepared pan, packing it down somewhat firmly with a spatula and smoothing the top; set pan aside.

In a large microwave-safe bowl (the same one is fine, no need to wash it provided you scraped it with a spatula fairly clean) combine chocolate chips, heaping 1/4 cup peanut butter, and heat on high power for 1 minute to melt.

Stop to stir. Chips may not be completely melted. Return bowl to microwave and heat in 10 to 15-second bursts until mixture can be stirred smooth.

Pour chocolate mixture over bars, smoothing the top lightly with a spatula or knife; set aside.

Add 1/4 cup peanut butter to a small microwave-safe bowl and heat to melt, about 30 seconds. Stir peanut butter smooth.

Evenly drizzle peanut butter over the chocolate and swirl it lightly with the tip of a knife or toothpick. To create the marbled pattern shown, drizzle peanut butter over the chocolate in 5 wide, evenly spaced, parallel lines, each spanning the width of the pan. Like 5 rows of long train tracks.

Rotate pan 90-degrees. With a toothpick, starting at the top of the pan, “draw” 5 evenly spaced lines through the peanut butter. You’re dragging the toothpick perpendicularly through the first set of lines to create the pattern.

Cover pan with a sheet of foil (to prevent fridge smells), and place pan in fridge to set up for at least 2 to 3 hours, or overnight, or until chocolate layer is completely set before lifting out with foil overhang, slicing, and serving.