1 1/2 cups old-fashioned oats (do not use instant or quick oats)
1 1/2 cups all-purpose flour
1 teaspoon baking soda
1/2 teaspoon baking powder
1/2 teaspoon salt
1 cup unsalted butter, room temperature
1/2 cup caster sugar
1/2 cup (packed) dark brown sugar
2 large eggs
2 teaspoons vanilla extract
1 12-ounce package dark chocolate chips
Preheat oven to 180 degrees C.
Butter 3 large (16 by 14-inch) nonstick baking sheets.
Place oats and 1/2 cup flour in processor; blend until oats are almost ground, about 10 seconds. Transfer oat mixture to medium bowl. Mix in remaining 1 cup flour, baking soda, baking powder and salt.
Using electric mixer on medium-high speed, beat butter in large bowl until light, about 1 minute. Add both sugars and beat until well blended, about 1 minute. Add eggs and vanilla; beat until well blended, about 1 minute. On low speed, beat in dry ingredients just until blended (do not over beat). Stir in chocolate chips.
Drop batter by 1/4 cupfuls onto prepared sheets, spacing evenly apart and forming 6 mounds per sheet. Bake cookies 8 minutes. Reverse cookie sheets and continue baking until golden brown, about 8 minutes longer. Cool cookies on sheets for 5 minutes. Using metal spatula, transfer cookies to racks and cool completely.