Preheat the oven to 325F and prepare baking sheets with parchment paper.
In a bowl, sift together flour, baking soda and salt.
In another bowl, cream together the butter, brown sugar and white sugar until light and fluffy. Then, add the vanilla, egg and egg yolk and beat it together with the butter and sugar mixture until well combined. Add the flour mixture and blend. Finally, add the chocolate chips, pecans, flax (if adding) and oats (if adding).
Roll a tablespoon of dough onto a ball and put on the baking sheet. Make sure to allow enough space in between the dough balls. Bake until golden brown for about 11 to 14 minutes. When baked, leave cookies on the baking sheet and place the baking sheet on a wire rack to cool until the cookies can be transferred onto a wire rack without breaking apart.
Recipe by sprinkles and sauce at https://sprinklesandsauce.com/chewy-chocolate-chip-pecan-cookies/