Preheat oven to 350˚F and grease the bottom of a 9” tart or cake pan. Set aside.
With a hand mixer or in the bowl of a stand mixer, whip the butter, brown sugar and cane sugar until fluffy.
Add the flaxseed and water mixture and vanilla extract and continue to mix until fluffy, about 1-2 minutes.
In a small bowl, mix the All-Purpose Flour Mix, baking soda, salt and guar gum. Add to the other bowl and mix together until your cookie dough forms. Stir in the Mini Chips.
With damp hands, press the dough into the prepared baking pan. Bake for 35 minutes or until lightly browned and cooked through.
While the cookie cake is cooling, prepare the frosting by mixing the butter and all but ½ cup of the powdered sugar. Add the vanilla extract and the dairy-free milk and whip until light and fluffy. Add more powdered sugar if necessary to reach desired consistency.
Frost top of the cooled cake and sprinkle with additional chocolate chips.