Line two baking sheets with a silicone mat or parchment paper. Set aside
Pour cornflakes into a large mixing bowl. Set aside.
In a medium saucepan, over medium heat, stir together sugar and corn syrup until combined. Cook for 3-4 minutes until the sugar dissolves. Do NOT boil. (the mixture will look white because of tiny bubbles. Lift some of the syrup up with a spoon to see if sugar is dissolved.)
Remove saucepan from heat and stir in peanut butter until evenly combined. Pour peanut butter mixture over cornflakes and mix until completely coated.
Drop heaping tablespoons of cornflake mixture onto prepared baking sheets. (I like to form them into little piles with my fingers if needed.) Let cookies rest for 30 minutes to set up.
To a microwave safe bowl, add chocolate and oil. Microwave for 30 seconds and then stir the chocolate. If needed, microwave for another 30 seconds and stir until chocolate is smooth.*
Drizzle chocolate over cookies. Let rest for another 15 minutes for the chocolate to set. (I like to refrigerate the cookies.) Serve immediately or transfer to an airtight container until ready to serve.
If your chocolate doesn't run off the spoon smoothly, add another 1/2 teaspoon of vegetable oil and stir until it's mixed in. This should thin the chocolate enough to let is drizzle. Do NOT add water or milk!
Recipe yield varies on how big you make your cookies. Don't be shy when portioning, there's plenty of the cornflake mix.