Prepare your flax egg by combining 2 tablespoons ground flaxseed with 6 tablespoons of water. Let sit for 10 minutes, for a gel to form.
Preheat the oven to 180C/350F. Line an 9 x 9-inch pan with parchment paper and set aside.
In a small bowl, add your flour, baking soda, and salt, and mix well. In a separate bowl, cream together your softened butter with sugars, using a stick mixer. Once smooth and creamy, add in the vanilla extract.
Gently add in the dry ingredients and mix until just combined. Using a rubber spatula, fold through your chocolate.
Transfer your cookie bar mixture into the lined pan and bake for 25 minutes, or until a skewer comes out clean. Remove from the oven and let cool in the pan completely, before slicing into bars.
Notes
* To make a flax egg, combine 2 tablespoons ground flaxseed with 6 tablespoons water. Let sit for 10 minutes, for it to thicken and a gel to form. Alternatively, you can use large whole eggs. ** Sugar free alternatives include monk fruit sweetener or erythritol. *** Use swerve brown sugar or golden monk fruit sweetener for a sugar free option. TO STORE: Cookie bars can be stored at room temperature, covered, for up to 1 week. Store them in the refrigerator if you'd like them to keep longer. TO FREEZE: Wrap bars in parchment paper and place them in a ziplock bag. Store in the freezer for up to 6 months.