To make the peanut butter Rice Krispies base:

Grease a 13"x9"x1" pan with cooking spray, cover in parchment paper, and spray again. Set aside (alternatively, you can use a 13x9x2" pan). Place the Rice Krispies in a large mixing bowl and set aside.

In a small microwave safe bowl, melt the butter and peanut butter in the microwave, checking on the mixture and whisking it with a fork or small whisk every 45 seconds. Once completely melted, add the vanilla and salt, whisk again, and set aside. (This can also be done on the stove.)

In a small saucepan over medium heat, gently stir the sugar and dark corn syrup together, until the mixture boils. Stirring constantly, allow it to boil for about 20 seconds. Remove the mixture from the heat and immediately add the melted butter and peanut butter mixture. Working quickly, stir well with a rubber spatula, ensuring the butter and peanut butter are completely incorporated into the sugar syrup mixture.

Once incorporated, pour the mixture over the Rice Krispies, scraping the sauce pan with a rubber spatula. Fold the mixture into the Rice Krispies until all of the cereal is evenly coated. Transfer the coated Krispies to the prepared baking pan. Place a piece of parchment paper over the Rice Krispies and press down (gently) on the paper with your hands, flattening the Rice Krispies, moving them into the corners of the pan, and ensuring that they are in a solid, even layer. Place the pan in the refrigerator to firm up.

To make the milk chocolate peanut butter ganache:

Place the chocolate, peanut butter, and corn syrup in a small heatproof bowl. Pour the cream into a small saucepan and heat it over medium to medium high heat on the stove top until bubbles form around the edges and just begin to form in the middle. Pour the warm cream over the chocolate and peanut butter and let the mixture sit for one minute. With a fork or small whisk, stir the mixture until the chocolate and peanut butter are completely melted. This may take more stirring than you'd think, but keep going until there are no more chunks of chocolate.

Remove the pan of Rice Krispies treats from the fridge, and pour the ganache over them. Using a small offset spatula, spread the ganache smoothly and evenly. Return the pan to the fridge for at least an hour. When ready to serve the treats, sprinkle flaky sea salt over the ganache, and slice into whatever size treat suits your fancy. The treats will keep covered in saran wrap in the fridge for 3 to 5 days.