Heat the oven to 350°F and line two baking sheets with parchment. Whisk the flour, baking soda, baking powder, and salt in a medium bowl until evenly combined.

Beat on medium speed for 2 minutes, until smooth and creamy, scraping the bowl once.

Beat for 30 seconds, until the dough looks glossy and no streaks of egg remain.

Mix on low speed in two additions until a few streaks remain, then finish with a spatula. The dough should look thick and soft, a little sticky but not wet.

Cover and refrigerate for 30 minutes, until firm enough to roll without sticking to your hands.

Portion about 32g of dough per cookie, roll each piece into a ball, and coat it in granulated sugar. Place the balls 2 inches apart, then press each one with a fork, once in each direction, to about 1/2 inch thick.

Bake at 350°F for 10 to 12 minutes, until the edges are set and golden and the centers look soft and slightly puffy. Sprinkle with flaky salt, then cool on the pan for 10 minutes.