Preheat oven. Preheat oven to 350 °F/177 °C. Line two baking sheets with parchment paper or a reusable baking mat.
Prepare the flax egg. In a small bowl, stir together the flaxseed and water. Set aside and let it sit for at least five minutes.
Combine ingredients. Using a rubber spatula, cream together the peanut butter, organic cane sugar, and vanilla extract in a large mixing bowl until completely combined. Then, stir in the flaxseed mixture until well mixed. Finally, stir in the all-purpose flour and baking powder.
Chill the dough. Chill the dough in the refrigerator for at least 30 minutes before baking. This step is optional but is recommended for best results. Chilling the dough prevents it from spreading too much in the oven, which would result in flat cookies.
Roll and press the dough. Scoop out dough and roll into 1” balls. Place them on the prepared baking sheet about 2” apart. Using a fork, press the balls down in a crisscross pattern. If your fork is sticking to the dough, dip your fork in sugar or flour before pressing to prevent this.
Time to bake. Bake cookies for 10-15 minutes on the top or middle oven racks. When finished baking, transfer to wire rack to cool. When you take them out of the oven, they will continue to cook while they cool on the wire rack. If you prefer soft and chewy cookies, bake for 10-12 minutes. If you prefer firm or crispy cookies, bake closer to 13-15 minutes.