Add all dry ingredients to a large bowl: pistachios, pecans, oats, chocolate chips, flaxseed, and salt, if using. Stir until well mixed.
Add all wet ingredients to a medium bowl: coconut sugar, coconut oil, almond butter, maple syrup, almond extract. Whisk until well incorporated.
Pour wet ingredients over dry ingredients. Using a rubber spatula, stir and fold until very well mixed.
Pour the mixture into the prepared baking pan. Using the spatula, press mixture firmly down into an even, very tightly packed layer.
Bake for 22-27 minutes. Mine took 25 minutes.
Place baking pan onto a cooling rack to cool for about 30 minutes, or until completely firm. After, lift bars and parchment paper onto the cooling rack to finish cooling for 1-2 hours. Slice and enjoy! Storing instructions below.