GF Homemade Chocolate Sandwich Cookies (fake Oreos)

So, it was my love of all things cheesecake that brought me to discover this recipe and start to modify it. I've posted it on my family blog before, but have since changed it, and I plan to tweak it again. These make such an excellent crust for cheesecakes requiring a chocolate cookie crust. I guess it was actually the frosting that got me thinking I could make a good oreo. For my daughter's first birthday, I made a chocolate cake. I wanted white frosting, but I didn't want a buttercream frosting with my chocolate cake, so I devised a plan to make white chocolate frosting by modifying one of my favorite recipes from Nigella Lawson. The frosting was an amazing success and I decided it would be the perfect filling to an oreo cookie. I went online and found a gluten free fake Oreo posted on the blog "Hey, that tastes good". I made them, and liked them, have now adjusted them slightly, and here we are now. I'm posting the recipe I used to make these exact cookies.

1/2 cup GF flour
3/4 cup Featherlight mix
1/2 cup unsweetened cocoa powder ( I used Hershey's Special Dark cocoa, so excellent!)
1/2 t xanthan gum
1 1/2 t baking soda
1/4 t baking powder
1/4 t salt
1 cup sugar
5 T unsalted butter, room temp
5 T butter flavored crisco
1 large egg plus 2 egg whites

Combine dry ingredients in a stand mixer. Add butter and shortening, in pieces, mixing on low until combined. Add eggs one at a time, then mix until incorporated. Drop by SMALL teaspoonfuls onto cookie sheet lined with parchment. After you've made uniform balls, press the cookies down flat (this time I was able to use the heel of my hand to push them down, but if the dough is too sticky, I've used the underside of a glass coated continually in powdered sugar) so they will be more like a thin oreo cookie.
It's best to make these small so the chocolate cookie doesn't overwhelm the filling. Bake at 350 for 6-8 minutes. (This temp/time combo makes a really crisp thin cookie, much like the actual oreo, but play around if you want it softer, or chewier, I know I do.)

Filling:
1 cup plus 2 T unsalted butter, room temp
2 cup powdered sugar, sifted (really, you should do it)
1 T vanilla
1/2 cup white chocolate chips, melted

Melt chips 1 min on high in microwave, mix until totally melted and smooth. Let sit. Beat butter until smooth. Add sifted powdered sugar. Once the butter and sugar and light and fluffy, add vanilla and melted chocolate. Mix well. Using a plastic bag with a half inch opening, pipe a generous teaspoonful of filling on one side, then top with a similar sized cookie and push together to even out the filling. This is a big amount of frosting, because they really taste great with a lot of filling. You can halve it if you'd like less. The cookies aren't very sweet, so putting them with a lot of filling makes for a great sweetness. This makes about 30 sandwich cookies.
Enjoy!