Line an 8x8 pan with parchment paper - making sure it goes up the sides of the pan.
Heat your oven to 350 degrees.
Place the flax in a small bowl and add 6 tbsp of room temperature water. Whisk, set aside, and then whisk every few minutes - about 5 times total.
Place the butter and chocolate chips in a small pot over very low heat. If you have a double boiler, use that instead - I don’t, so I just use a small saucepan. Watch the butter and chocolate so it doesn’t burn, and as it begins to melt, stir together using a rubber spatula. It’ll melt in just a few minutes, so don’t go too far!Remove from heat and set aside, allow it to slightly cool. In a small mixing bowl, combine the flour, cocoa, and salt. Then stir in the baking soda, and set aside. Pour the chocolate/butter mixture into a larger mixing bowl. Stir in the vanilla and flax and combine well, then stir in the sugar. Mix really well!
Slowly stir in the flour mixture, pouring about 1/2 in and mixing well, then pouring the rest, mixing until all clumps are gone.
Pour the batter into your prepared pan, and bake on the middle rack at 350 for 35-40 minutes, until the edges begin to crisp.
Let cool completely for 30 minutes, then slice and enjoy!