Preheat oven to 300 degrees. Line cookie sheets with silicone liner or parchment paper. Combine 2 cups of the oats in your blender or food processor and process until finely ground and floury, set aside. In a large mixing bowl, beat the butter until light and fluffy, add brown sugar and continue beating combining well. Add eggs one at a time mixing well after each addition, then add the vanilla and mix well. (Scrape bowl down once or twice to combine evenly.) To the bowl that has the blended oats, add the remaining 1 cup oats, baking soda, and salt, stirring to combine. Add this oat mixture to the butter mixture stirring to combine. Stir in the mini chocolate chip pieces.
Drop the dough by rounded spoonfuls approximately 3 inches apart onto the prepared cookie sheets. (They will spread during baking.)
Bake for 13 to 15 minutes (until lightly browned). Cool completely on the sheets before removing to racks.