Make the batter first. In a medium sized mixing bowl, sift together the flour, baking powder, baking soda and salt. Set aside.
In a small bowl make a flax egg by whisking together the flax and the water. Set aside to thicken while you prepare the rest of the batter. Let it sit for at least 2-3 minutes.
Now in a large mixing bowl, whip together the vegan butter and sugar using a hand mixer or a stand mixer. Mix until combined.
Then add the vanilla and flax egg. Continue to mix until combined.
Next, add the dry mixture and the non-dairy milk to the butter mixture alternating between the dry mixture and milk until everything is fully incorporated.
Now, fold the blueberries into the batter.
Spray a whoopie pie pan with non-stick spray and fill the pan dividing the batter evenly into 12.* Wet your finger and smooth out the batter.
Chill for 15 minutes while you preheat the oven. Preheat the oven to 375 degrees(F).
Then bake for 12-15 minutes or until golden brown. Let cool completely.
While they are cooling, make the frosting. Crush the freeze dried strawberries and raspberries either in a food processor or by putting them into a large plastic bag and smashing. Set aside.
Now, in a large mixing bowl, beat together the vegan butter and vegetable shortening. Then add the powdered sugar a little at a time, continuing to beat until all the sugar has been incorporated. It will be thick.
Then add the milk, vanilla and salt. Combine. Make sure the frosting is now light and fluffy and firm.
Next, fold the freeze dried berries into the frosting. Chill until ready to use.
Once the blueberry pies are cooled , spread frosting on the inside of one and a little more frosting on another and sandwich together. Repeat with all of them to make 6 sandwiches.
Keep in the fridge.
Notes
*If you don't have a whoopie pie pan, line 2 baking sheets with parchment paper and make 12 round cookie sized circles, dividing the batter evenly, 6 on each pan. Then smooth out with your finger and chill for about 20 minutes instead of 15.