Line a 9-inch square pan with two large pieces of parchment paper, creating a sling for easy removal.

In a medium bowl combine the flour, powdered sugar, and salt.

Cut the cold butter into cubes and toss in the flour. Using your fingers, cut the butter into the dry ingredients until pea sized pieces are left.

In a small bowl, whisk together the egg yolk and milk. Add to the dough, and use a rubber spatula to mix until cohesive dough forms.

Add the dough to the prepared pan and use another piece of parchment paper to press it into an even layer. Use the back of a spoon or small measuring cup to pack it in and level it out. Place in the fridge to chill for 30 minutes.

Near the end of the chill time, preheat the oven to 350 degrees F.

Dock the chilled dough with the tines of a fork.

Bake the shortcrust pastry for about 18-20 minutes or until the edges are lightly golden and the center no longer looks doughy. Set aside to cool completely.

In a medium pot, combine the fresh quartered cherries, sugars, and salt. Place over medium heat, stirring occasionally for about 10 minutes or until the cherries start to soften and release their juices.

Add the cornstarch and cook for another 10 minutes until the cherries have softened and the juices have thickened. Remove the pot from heat and stir in the vanilla.

Spread the cherry filling out onto a small baking sheet and place in the fridge for a few minutes to cool. Alternatively, pour the cherry filling into an airtight container and chill in the fridge overnight.

In a medium bowl, combine the flour, oats, brown sugar, and salt.

Add the cubed butter and toss to coat. Rub the mixture between your fingers until it resembles wet sand and there are no visible pieces of butter left.

Cover the bowl and place in the fridge until ready to use.

Preheat the oven to 350 degrees F.

Pour the chilled cherry filling onto the cooled shortcrust pastry, and smooth it out with an offset spatula.

Sprinkle the oat crumble on top, then bake for 35-45 minutes until golden.

Allow the cherry pie bars to cool completely before cutting into 16 squares.