Preheat oven to 350 degrees F. Line baking sheets with parchment paper, if desired, and set aside.
Mix flaxseed with water in small bowl and let soak for 5 minutes.
Beat butter, white sugar, and brown sugar together in a large mixing bowl until creamy. Add egg yolks and vanilla extract; beat to incorporate, scraping down the sides as needed. Mix in the flaxseed mixture.
In a separate large bowl, whisk together flour, brewer's yeast, wheat germ, baking soda, salt, and cream of tartar; add to butter mixture and mix until just combined. Fold oats and chocolate chips into the dough.
Drop walnut-sized dough balls and place 2 inches apart onto a baking sheet. Bake 10 to 12 minutes or until edges are slightly golden. Allow the cookies to cool slightly on the baking sheet before removing to a wire rack to cool completely.
Notes
To make these as an oatmeal cookie without lactation perks, omit the brewer's yeast and increase the wheat germ to 3 tablespoons.