Preheat the oven to 350 degrees F.
In a medium bowl, combine the oats, flour, ground flaxseed, baking soda, cinnamon, baking powder and salt.
To the bowl of your Kitchenaid (or in a separate bowl), add the butter, sugar and brown sugar. Beat for 3-4 minutes, until creamy and fluffy. Then add the egg, egg yolk and vanilla and beat until combined.
Add the dry ingredients to bowl and beat until combined.
Fold in the chocolate chips.
Scoop the dough into 1-inch balls out and place on the baking sheet 2-3 inches apart. Flatten cookies to desired thickness before baking (they stay roughly the same shape). Top with more chocolate chips if desired.
Bake for 10 minutes then let cool on pan for 5 minutes before transferring to a wire rack to finish cooling.
