For the crust, combine flour and salt in a big bowl. Cut in butter until coarse crumbs form. Combine egg yolk and milk then gradually add to flour mixture and work with hands until dough forms. Divide dough in half.
Preheat the oven to 350°. Roll one piece of dough into a thin 14 x 19ʺ rectangle. Transfer to a half sheet pan (about 10 x 15 x 1ʺ) and press into corners and up the sides, leaving a 1ʺ overhang. Sprinkle cornflakes over the bottom and set aside.
Put all filling ingredients into a bowl and toss to mix with one of Rada's Mixing Spoons; transfer the mixture evenly into the crust with a larger Basting Spoon. Roll the remaining dough into another big rectangle and place it over the apple filling. Moisten the edges, pinch crusts together, and crimp as desired around the rim of the pan.
Brush egg white over the top crust and sprinkle with cinnamon-sugar. Bake for 45 to 55 minutes, until golden brown.
For the glaze, grab a whisk (try Rada's Handi-Stir) to combine the powdered sugar, vanilla, and enough milk to make a drizzling consistency. Drizzle over warm pastry and cool completely. Cut into bars and use Rada's non-scratch Slotted Turner or Potluck Spatula to remove them from the pan.
*Try Granny Smith, McIntosh, and/or Jonathan apples. Here's your opportunity to put the Rada Paring Knives to work.