In a small bowl, whisk ground flax and water. Set aside to allow thickening.
In medium bowl, whisk flour, salt, baking powder and baking soda.
In a large bowl, beat butter and both sugars. Add flax mixture and vanilla, continue to beat until thoroughly mixed.
Slowly beat in the flour mixture, half cup at a time until thoroughly mixed. Do not overmix! Fold in Chocolate pieces.
Place bowl of batter in the refrigerator for 30 min.
Preheat oven to 350°.
On parchment-lined baking sheets, use a small cookie scoop to make approx 24 cookie balls. Use a spatula to slightly press each ball. Lightly dust the cookies with flake salt.
Bake for 12 - 14 minutes, or until edges start brown and centers are puffed up.