1. Adjust oven racks to the upper-middle and lower-middle positions. Preheat oven to 350°. Grease cookie sheets or line with parchment paper.
2. In a medium bowl, whisk together flour, baking powder, baking soda and salt. Set aside.
3. In a large mixing bowl, cream together the butter, granulated sugar, and brown sugar. Beat in the eggs one at a time, mixing well after each addition. Mix in the vanilla extract.
4. Gradually beat in the flour mixture, mixing only until dough comes together. Do not overmix.
5. With a large wooden spoon or rubber spatula, stir in the rolled oats, followed by the chocolate chips.
6. Using a large cookie scoop (by weight, the balls of dough should be about 2 oz. each), drop the cookies on the prepared cookie sheet about 2 inches apart (I usually fit 9 on my cookie sheets). Bake until the cookies are slightly browned and set on the outside but still soft and puffy in the middle, about 14 minutes, rotating the baking sheets front to back and top to bottom halfway through the baking time. Cool the cookies completely on the baking sheets.