Lightly grease a 9-by-13-inch baking dish with cooking spray. Line with parchment paper, leaving an overhang on the sides.

Whisk together the ground wafers, oats, sugar, and salt in a large bowl. Set aside.

Melt the butter in a medium heavy saucepan over medium heat, then add 1 3/4 cups peanut butter, whisking until well combined. Pour the peanut butter mixture over the wafer mixture, stirring until combined. Transfer to the prepared baking dish, and firmly press the mixture into an even layer. I used a piece of parchment to do this; the original recipe suggests a measuring cup.

Refrigerate for 30 minutes.

Pour melted semisweet chocolate over the chilled bars and use an offset spatula to spread it into an even layer that covers the entire surface of the bars. Refrigerate until hardened, at least 15 minutes.

Melt the milk chocolate in a small saucepan. When it is partially melted, add the remaining 2 tablespoons of peanut butter and whisk smooth. Pour over the chilled bars and again use an offset spatula to spread the milk chocolate mixture evenly over the bars. Chill another 15 minutes.

Use the parchment to lift out the entire chilled block of bars. Run a sharp knife under hot water, dry well, and slice the bars into desired size rectangles, wiping the knife between cuts. Let bars stand at room temperature for 10 minutes before serving. I kept the bars at room temperature, but if your kitchen is warm you may need to store them in the fridge.