Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together the all-purpose flour, baking soda, ground cinnamon, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Stir in the rolled oats, ground flaxseed, brewer’s yeast, and raisins until evenly distributed.
Drop tablespoon-sized portions of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are golden brown but the centers remain soft.
Remove from the oven and allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.