Preheat the oven to 350°F and line a 9×13-inch baking dish with aluminum foil and set aside. In a stand mixer fitted with a paddle attachment, cream together the butter and sugar. Add in the flour, corn starch, and salt, beating slowly at first then increasing to medium-high speed for 3 to 4 minutes until the dough pulls away from the sides of the mixing bowl and is no longer crumbly. Press dough evenly into the prepared baking dish and set aside.
When the cookie/brownie layer is about 10 minutes from being done, add the caramels and the heavy cream to a small saucepan and melt over medium heat, stirring constantly until candies are completely melted. Remove the cookie/brownie layer from the oven when ready and pour the caramel sauce evenly over the brownie layer. Chill in the fridge for 1 to 2 hours until caramel is stiff to the touch.
Make a half batch of my Peanut Butter Frosting and evenly spread it out over the top of the hardened chocolate layer. Sprinkle with chocolate sprinkles. Gently lift the bars out of the pan by gripping the aluminum foil, I recommend picking one side of the bars to lift up while sliding the baking dish in the opposite direction so your bars are always close to the counter. Use a sharp knife to cut into squares for serving.
Store in an air-tight container in the refrigerator for up to 1 week. They may be left at room temperature but should be consumed within a couple of days.