Cut the butter into 6 pieces and put it in a small sauce pan over medium heat. Once the butter melts, a layer of foam will appear on top and it will make some popping noises as the water in the butter is cooked off. Stir the melted butter often to see what color it is under the foam. After a few minutes, the noise and foam will subside, the melted butter will be a beautiful brown color, and it will have a nutty aroma. Once this happens, pour the butter into a small heat proof bowl to stop the cooking process and allow it to cool.
6 TBS butter
Put the flour and dates into the bowl of a small food processor. Process for at least a minute or longer. Process until the dates and flour resemble wet sand. Pulse in the salt, baking powder, and baking soda.
1 cup whole wheat flour, 1 cup pitted Medjool dates, ¾ tsp salt, ½ tsp baking powder, ¼ tsp baking soda
In a large bowl, combine the cooled brown butter, peanut butter, egg, and vanilla together until thoroughly mixed.
⅓ cup unsweetened natural peanut butter, 1 whole egg, 2 tsp vanilla
Add the dry ingredients in with the wet ingredients. Stir until there is no more dry flour.
Cover and chill the dough for 15 - 30 minutes in the refrigerator.
Place an oven rack in the center position and heat the oven to 350℉.
Portion the chilled dough into 12 even balls (~ 43 grams each). Flatten each ball into a disc between your palms, using the warmth of your hands to press the dough together (the dough is slightly crumbly). Place discs 1" apart on a lined cookie sheet.
Using a fork, carefully make the signature criss cross pattern on the top of each cookie (be aware that if you press the dough too hard with the fork it will stick to the fork. Be very gentle when making the cross hatch pattern or skip it altogether).
Bake for 13 - 15 minutes, until the center is set. Remove from the oven and immediately sprinkle with flaky salt. Let cool for 10 minutes on the cookie sheet, then remove and continue cooling on a wire rack.