Heat the oven to 350 degrees. Grease a mini muffin tin or use paper liners. (I prefer to use parchment paper cups for easy cleanup.)
In a small bowl, mix the ground flax with the water. Set aside for 5 minutes. (If using an egg instead, just add that to the bowl with the other ingredients in the following step.)
In a large bowl, add the almond butter, sweet potato puree, brown sugar, vanilla, and flax mixture. Stir well to combine.
Stir in the baking soda, salt, cocoa powder, flour, and mini chocolate chips. The batter will be very thick.
Scoop the batter into the mini muffin tin. Top each brownie with a few more mini chocolate chips, if you'd like.
Bake until just set, 14 to 16 minutes. The brownies should still look a little undercooked/molten in the center.
Allow to cool then remove the brownie from the pan. Store brownies in an airtight container at room temperature for 2 days or in the refrigerator for 5 days.