1. Preheat the oven to 350 F and line a 9×13 pan with aluminum foil – leave enough hanging over the sides so you can easily grab and lift the bars out of the pan later. Spray with non-stick spray and set aside.
2. In a large bowl, whisk together the flour, baking powder, cornstarch and salt.
3. In the bowl of a stand mixer with the paddle attachment, or using a hand mixer, cream the butter and brown sugar together until light and fluffy. With the mixer running on low, add the eggs one at a time. Scrape down the sides of the bowl with a spatula, as needed. Add in the vanilla and mix until incorporated.
4. With the mixer running on low, slowly add in the dry ingredients to the wet until fully incorporated. Using a spatula, fold in the crushed cookies.
5. Press the batter evenly into the pan. Bake for 20-22 minutes.* Let the bars cool for at least 15-20 minutes before grabbing the edge of the foil and lifting the bars out of the pan. Cut into 24 bars.

Bars will keep at room temperature, in a sealed container, for up to 2 weeks, or in the freezer for up to 2 months.