In a food processor, combine flour, cold butter, egg yolk, milk, and salt until the mixture forms a cohesive dough. Chill in the refrigerator for at least 30 minutes.

Preheat your oven to 350°F (175°C). Grease a 13x9-inch baking pan. Press half of the dough into the bottom of the pan.

Peel and slice the Granny Smith apples, then toss with vanilla, sugar, flour, and cinnamon. Set aside for 10 minutes.

Spread the apple mixture evenly over the prepared dough in the baking pan.

Roll out the remaining dough and place it over the filling. Seal the edges and brush with egg wash. Sprinkle with turbinado sugar.

Bake for 35-40 minutes until golden brown and filling is bubbling. Let cool before slicing.

Allow the bars to cool completely on a wire rack for about 30-60 minutes before serving.