Line a 9x13 pan with parchment. You won't bake it in this pan, but this will form your cookies for chilling.
Combine the all-purpose flour, whole wheat pastry flour, cornstarch, and salt. Mix and set aside.
Cream butter and sugar with a hand or stand mixer for about 2- 3 minutes until it is light and fluffy. You can also do this by hand, just know you will really be working your arm muscles! Add in the dry ingredients and mix to combine.
When you add in the freeze-dried raspberry powder, I like to mix it in by hand. This gives it a marbled effect that I think is so pretty.
Once it is mixed in, press it into your 9x13 pan. When it is in the pan, cut it into the size of bites you want. Mine were a little bigger than an inch. These do not need to be perfect, so don't stress. I used a bench knife to cut mine, it really is so easy.
While it is chilling, line 2 baking sheets with parchment paper.
Preheat the oven to 300 degrees.
When you remove it from the fridge. Remove the parchment paper from your 9x13 pan and the cookies with it. Pull the bites apart and place them on your baking sheets. These will spread just a little bit, so give them a bit of space. Not much, but a little bit.
Place in oven and bake for about 7-10 minutes until the edges are a VERY light golden brown. You don't want to overbake these.
Remove them from the oven and set them on a cooling rack. These cookies can be eaten right away, cooled, or even saved for later. They are good at room temp for up to 3 days. They are good in the fridge in an airtight container for up to a week. Or if you want to freeze them, place them in a ziplock bag and they hold well for up to 3 weeks!