Make the Bars:
Line an 8×8-inch square pan with aluminum foil, spray with cooking spray; set aside.
To a large microwave-safe bowl, add 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. Stop to stir.
Return bowl to microwave and heat for 30 more seconds on high power. Stop to stir. (That was 2 1/2 minutes total microwave time)
Stir in the vanilla. (1 tablespoon is 3 teaspoons, use less if you prefer less vanilla flavor)
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.
For the Topping:
To a medium microwave-safe bowl, add the chocolate chips, peanut butter, and heat on high power for 30 seconds. Stop to stir. Heat in increments of 20 to 30 seconds, stopping to stir after each 20 to 30 second increment until chocolate has melted and can be stirred smooth. It will probably take 1 1/2 to 2 minutes total.
Evenly pour chocolate mixture over Special K layer, smoothing the top lightly with a spatula.
Evenly place the candy pieces over the top. Add as many as you like (I’m generous) and use your favorite candy including Snickers, Turtles, Milky Way, 3 Muskateers, Payday, etc.
Cover pan with foil and allow bars to cool at room temp until chocolate has set, likely 4+ hours. I don’t like to refrigerate them because the chocolate topping and the candy bars can sometimes turn color (bloom) or experience condensation droplets when brought back to room temp however these are purely cosmetic issues, won’t effect taste, and will speed up the cooling process if you’re in a hurry.