Preheat oven to 350 degrees, line the bottom of a 9×13 inch pan with parchment paper, set aside. PREPARING THE DOUGH In a large bowl whisk together the flour, sugar and salt. In a separate bowl whisk together the egg yolk and ice water. Slowly pour into the flour mixture, mixing until combined. Cut the butter into the mixture with a pastry blender until pea-size clumps form. Knead the dough into a ball, then pat flat and wrap with plastic wrap. Refrigerate for 30 minutes. PREPARING THE FILLING Meanwhile, slice the peaches, remove the skin and combine them along with the flour, cornstarch, brown sugar, cinnamon, vanilla, and lemon juice in a large bowl, toss together to coat evenly. After the dough has chilled, roll it out into a 9×13 inch rectangle. Place in the bottom of the prepared pan. PREPARING THE CRUMB TOPPING In a medium size mixing bowl, combining the oats, flour, brown sugar, cinnamon, and salt, whisk together. Using a pastry blender, cut in the cold cubed butter until small clumps form. Pour the peach mixture into the pan over the pastry dough. Press to create an even layer. Pour the crumb topping over the peaches. Place in the preheated oven and bake for 35-45 minutes or until the top begins to brown. Remove from the oven and allow the bars to cool for 45 minutes before cutting and serving. The parchment paper should help prevent anything from sticking to the bottom of your pan.