Preheat the oven to 350 F and prepare an 8x8 inch pan with parchment paper. Start by making the cookie dough layer and placing the ground flax and water into a bowl, stir and set aside to gel.
In mixing bowl, use a handheld mixer to beat the butter, brown sugar and cane sugar until light and fluffy, about 1-2 minutes. Add in the vanilla extract and flax mixture and continue to mix until well blended, about 30 seconds. Add in the gluten free baking flour, baking powder baking soda and salt and mix until the dough comes together. Fold in the chocolate chips and press the dough evenly into the bottom of the pan. Bake for 5 minutes and then remove from the oven.
Separate the sandwich cookies so you have 16 cookie halves. Top the cookie dough layer with the Oreo halves and set aside.
In a bowl, stir together the gluten free baking flour, cocoa powder, espresso powder, baking soda and salt and then set it aside. Warm the coconut milk in a heat proof bowl in the microwave until scalding. Add in the chocolate chips and let them sit for 5 minutes before stirring smooth. Add in the butter, vanilla and brown sugar and mix until well combined. Finally stir in the dry ingredients until a batter forms. Spread the brownie batter evenly over the Oreo layer and bake the brownies for 17-20 minutes. Don't over bake or you will lose the "fudgy" factor of these brownies.
Let the brownies cool at room temperature for 30 minutes before refrigerating for 2 hours. Serve after refrigeration.
For super fudgy brownies, don't cook them longer than 20 minutes and be sure to refrigerate before serving. Enjoy!