Preheat the oven to 350°F (175°C) and line the bottom of a 4x7-inch baking dish with parchment paper.

In a small bowl, prepare the flax egg: whisk together the ground flaxseeds with the 3 tablespoons of water and let it sit for 5 minutes. It should become thick and viscous.

In a large mixing bowl, whisk together the almond flour, coconut flour, coconut sugar, and baking soda. Add the flax egg, almond butter, coconut oil, and vanilla extract. Mix using a spoon or spatula until combined. It should have the texture of cookie dough.

Stir in the dark chocolate chunks and roasted pistachios and mix again until combined.

Transfer the dough to the prepared pan and press it down into an even layer. You can use a layer of parchment paper and a glass to press it down if the dough is too sticky.

Bake for 10-12 minutes, or until the top of the blondies is slightly golden brown.

Remove from the oven and let it cool completely before cutting into small squares. Blondies will keep at room temperature in an airtight container for up to 5 days.