Mix together the flax and water and let sit until thickened, about 5-7 minutes.
In the bowl of a stand mixer, cream together the butter and sugars until light and fluffy.
Add the flax, vanilla extract, and water.
Sift together the dry ingredients and add to the mixer gradually.
Fold in the chocolate.
Using a 1/3 cup measurement, scoop the dough into large balls. Place 4-6 on a foil-lined pan (dull side up) and chill in the freezer for 15 minutes. Place them several inches apart from each other, these cookies spread!
Bake the chilled cookies for 10 minutes until slightly puffy in the center.
Lift the side of the baking sheet up about 4 inches and gently let it drop down against the oven rack so the middle deflates.
Bake for 2 minutes, then repeat the process of lifting and dropping the pan. Repeat this process a few times (bake 2 minutes, drop the pan) for 18 minutes total until the cookies have spread and the edges are golden brown.
The cookies are meant to be large. If you try to make them smaller, they won't get the ridges on the edges. Make sure to freeze the cookies for 15 minutes before baking, otherwise they will spread too much and won't get the ridges.