Combine the flour, salt, baking powder and pumpkin pie spice in a medium mixing bowl, set aside.
In a large mixing bowl, combine the butter, brown sugar and granulated sugar.
Add the vanilla, egg and egg yolk, then stir by hand or use an electric hand mixer to combine.
Add the flour mixture and blend until well combined.
Hand mix in the white chocolate chips.
Place 18 rounded balls of cookie dough on a baking sheet or baking stone.
Place in the oven and bake for 15-18 minutes.
Cookie dough: extra cookie dough can be stored in the refrigerator for 1 week or in the freezer for 9-12 months. I recommend storing the dough in the freezer already portioned into cookie dough balls. You can then take the balls of dough straight from the freezer to a baking sheet, adding and extra 2 minutes to the baking time.
Chocolate chips: semi sweet chocolate chips can be used in place of the white chocolate chips or chocolate chips can be omitted all together in this recipe.