Preheat oven to 350 °F. Grease a square 9x9 pan with vegetable oil or coconut oil.
Mix the ground flax seed and water in a small bowl, and allow to sit for 5 minutes to thicken.
Add all the ingredients (including the flax egg) in a blender or food processor, and blend until everything is well-mixed and smooth.
If you are using a blender and the mixture is too thick, add one tablespoon of almond milk to thin it. Make sure to mix it with a spoon
Once mixed, add the nuts to the batter, and transfer to the pan. Bake for 30 minutes. After 30 minutes, the brownies will still be soft, but allow it to cool to room temperature.
Once cooled, chill it in the refrigerator overnight and serve the next day.
Notes
This type of brownie is the soft, gooey, chewy type. It's not your standard non-vegan brownie.If you don't want to chill it overnight and eat it the same day it's baked, I suggest adding 1/2 cup of flour (whole wheat or all-purpose) to the batter. This will make the brownie set better while baking. Bake until there is only a few crumbs when you insert a toothpick in the middle, approximate 20 minutes.Also, if you like it sweeter, I suggest to add 5-6 tbsp of agave instead of 4 tbsp; however, don't go overboard on the agave because it is MUCH sweeter than sugar.
Substitutions:
You can use store-bought egg replacer instead of flax egg.
On the other hand, the flax egg is optional if you don't have it.
If you don't have agave syrup, substitute 2 tbsp of sugar for every tablespoon of agave syrup.