Mix together the flax and water and let sit until thickened, about 5-7 minutes.
Cream together butter and sugars until light and fluffy, about 5 minutes.
Add flax and vanilla and continue creaming for 2 minutes.
Sift together the dry ingredients (flour, baking soda, salt) and add to the mixing bowl. Mix until just combined, then add the chocolate chips.
Chill the dough for at least one hour. Once the hour is almost up, preheat oven to 350ºF.
Scoop the cookies onto a parchment-lined baking sheet, then chill the baking sheet for 10 minutes before putting in the oven. The cookies should be chilled before baking so that they stay tall and don't spread too much.
Bake the cookies 15-17 minutes until golden brown.
You can chill the dough for up to 72 hours before baking. The longer you let the dough chill, the more flavorful the cookies will be!