Preheat the oven to 350 degrees F. Lightly grease an 8 by 8 baking dish and set aside.
In a large bowl, mix together apples, sugar, cornstarch and apple pie spice. Set aside.
In another large bowl, mix together the dry ingredients.
Cut in the cold butter until pea-sized butter chunks are left.
Stir in 1 egg until the dough begins to resemble coarse sand.
Divide the dough in half and press one half into the bottom of the prepared pan.
Spread apple filling in an even layer over the dough, then crumble the remaining dough on top.
Bake for 38-40 minutes or until it is golden brown and the apples are booked. Cool completely before topping with glaze.
In a small bowl, whisk together buttermilk and sugar. Spread over cooled bars.