Heat oven to 375F. Spray a large cookie sheet with nonstick cooking spray or line with parchment. Set aside.
In the bowl of an electric mixer, beat the butter on medium speed until smooth, about 30 seconds to 1 minute. Add in the sugar, brown sugar and flax seed and beat until fluffy, about 2 minutes more, scraping down the sides of the bowl as necessary.
Beat in the eggs, one at a time, followed by the vanilla.
In a large bowl, combine the flour, whole wheat flour, baking soda and brewer's yeast. Add dry ingredients to butter mixture and beat until just combined. Beat in the oats, followed by the dark chocolate chips and nuts.
Spoon dough by heaping tablespoons onto baking sheet. Bake 8 to 10 minutes or until golden brown around the edges. Cool 5 minutes on baking sheet. Cool completely on wire cooling rack.
Recipe by Espresso and Cream at https://www.espressoandcream.com/2015/02/lactation-cookies.html