Step 1

Beat the butter in the bowl of a stand mixer or handheld electric mixer for a few minutes on medium-high speed until light and fluffy. Stop to scrape down the sides of the bowl.

Step 2

Add the brown and granulated sugars, baking powder, baking soda and cinnamon, beating on medium speed until the mixture is well blended. Reduce the speed to medium-low; add the eggs and vanilla extract, mixing until well incorporated.

Step 3

Reduce the speed to low; add the oats and flour and oats, stopping to scrape down the sides of the bowl as needed and mixing just until incorporated. Cover the bowl and refrigerate the dough for at least 1 hour, until needed.

Step 4

Position a rack in the middle of the oven and preheat to 375 degrees. Line a large sheet pan with parchment paper.

Step 5

Form the dough into golf ball-size balls and place about 2 inches apart on the prepared sheet. Sprinkle generously with flaky salt.

Step 6

Bake one sheet at a time for about 15 minutes, or until the cookies are puffed and beginning to turn golden, being careful not to overbake. (The cookies should have a tender interior.) Transfer the cookies, still on the parchment paper, to a wire rack to cool completely.