Preheat the oven to 300 degrees F.
Line a sheet pan with parchment paper or a baking mat.
Put 2 cups of the oats in the food processor and pulverize until finely ground and floury.
In a mixer fitted with the paddle attachment, cream the butter until soft and smooth. Mix in the brown sugar. Add the eggs and vanilla and mix until well blended.
In another bowl, stir together both the ground and the whole oatmeal, the baking soda and salt.
With the mixer running at low speed, add the dry ingredients to the butter mixture and mix until just blended. Add the chocolate chips and mix just until blended. (The cookie dough can be made and kept refrigerated for up to 3 days before baking. Or you can make lumps of dough and freeze them in a locked plastic bag, then take them out for baking a few at a time. Add an extra minute to the baking time.)
Drop the batter by teaspoonfuls onto the pan, leaving 3 inches between them, as they will spread. Bake until lightly browned, about 13 to 15 minutes. Let cool on the pan, then remove with a spatula.