Preheat oven to 350 degrees F. Line a baking sheet with parchment paper or a silicone mat.
In a small bowl, make the flax eggs by combining the ground flaxseed and water. Let it sit for 5 minutes to thicken.
Add the softened butter, brown sugar, and cane sugar to the bowl of your stand up mixer (I used my KitchenAid). Cream for 3 minutes. Add the flax eggs and vanilla and cream for another 30 seconds.
Add the flour, baking powder, baking soda, and salt to the mixer. Mix on low until combined, scraping down the sides. If the dough is too crumbly and not coming together, add 1 Tbsp of almond milk. It should be a thick dough.
Add the chocolate chips and hazelnuts. Mix until everything is evenly combined.
Place a large scoop of cookie dough onto the pan (mine were big, about 2.5-3 Tbsp). Top with more chocolate chips and hazelnuts if desired. Bake for 10-15 minutes, depending on how big you made your cookies. They will be slightly golden brown. Sprinkle some flaky sea salt on top. Let it cool on the pan for 15 minutes. Then transfer cookies to a cooling rack to cool completely. Enjoy!