Preheat oven to 400F°. Grease a 12x17 jelly roll pan.
In a large bowl combine all of the ingredients for the crust. Using a pastry cutter or a fork work everything together (like you would a pie crust). Once everything is combined divide the dough in half. Using your fingers press 1/2 of the dough into the prepared pan. It will be thin, that is ok. Sprinkle the corn flakes evenly over the crust.
In a separate bowl toss the apples, sugar and cinnamon together. Once well coated, spread the apples evenly over the crust. Cover with the remaining crust. It can be a little sticky, so I roll out small portions and place it on top. Kind of like patchwork :)
Bake for 10 minutes a 400F°. Turn down the oven to 350F° and bake for 40 more minutes. Remove from the oven and allow to cool. Once cool you can frost, if using (which you really should).
Mix everything together, and adjust the amount of milk to get a thin and almost drizzle-able frosting.
Apple Bars - https://www.bakedbyrachel.com/apple-bars/