Step 1

In a medium bowl, whisk together the flour, oats, baking powder, baking soda, and salt.

Step 2

In a large bowl, whisk the melted butter, sugar, and vanilla until smooth and homogeneous. Add the egg and whisk until fully combined and creamy. Add the dry ingredients and use a flexible spatula to stir until almost no flour is visible. Add the dates and stir until completely combined.

Step 3

Line a baking sheet with parchment. Scoop the dough into eight 2" balls (about 80g each; a level scone and muffin scoop works well here) and place on the prepared baking sheet. Cover and refrigerate for at least 1 hour and up to 2 days.

Step 4

Preheat the oven to 375°F with a rack in the upper third. Shape the dough mounds into neater balls by rolling between the palms of your hands. Return to the baking sheet, spacing them evenly.

Step 5

Bake the cookies for 13 to 16 minutes, until puffed, with golden-brown exteriors. Remove the baking sheet from the oven and immediately use a flat spatula to press each cookie flat, eliminating any puffing.

Step 6

Return the cookies to the oven, turn the oven off, and leave inside for 4 to 5 minutes, until the cookies are slightly darker and have puffed back up.

Step 7

Remove the baking sheet from the oven, press the cookies flat again, then sprinkle with flaky salt. Let the cookies cool completely on the baking sheet before serving.

Step 8

Store oatmeal-date cookies airtight at room temperature for up to 5 days; freeze for longer storage.