1. Preheat oven to 325°F. Position a rack in the center of the oven.
2. In a medium bowl, whisk together the flour and baking soda. Set aside.
3. In a medium saucepan over medium heat, melt the butter. Use a larger pan than you think you need to prevent overflow. Once melted, increase the heat slightly and let the butter simmer. It will become foamy as the milk solids separate. Stir frequently and watch closely to prevent burning.
4. When the butter turns golden brown and has a nutty aroma, remove it from the heat. Let it cool slightly, then transfer to a bowl to solidify at room temperature. Do not strain out the browned bits as they add flavor. (This step can be done in advance; store browned butter in the fridge and bring to room temperature before using.)
5. In a stand mixer fitted with a paddle attachment (or using a hand mixer), cream the cooled, room temperature browned butter with both sugars until light and fluffy. Mix in the vanilla extract.
6. Add the dry ingredients and mix on low speed just until combined. Do not overmix. Gently knead the dough in the bowl to bring it together.
7. Let the dough rest for 30 minutes to help it hold its shape. Note: If the dough feels too crumbly, add 1 tablespoon of melted butter (does not need to be browned) and mix it in for additional moisture.

Shaping the Cookies

1. At Metropulos, we made these cookies in two sizes, but the mini size is particularly fun.
2. Use a 1-inch cookie scoop for small cookies or a 2-inch scoop for larger ones.
3. If you don’t have a scoop, pinch off a piece of dough and roll it between your palms to form a tight ball, a little smaller than a golf ball.
4. Arrange the dough balls on a parchment or silicone-lined baking sheet, spacing them 2 inches apart. Gently press each ball into a flat disk, smoothing the edges to retain their shape.
5. Bake small cookies for 7-9 minutes and large cookies for 10-12 minutes.
6. The cookies are done when they just begin to turn golden brown.
7. Remove from the oven and immediately sprinkle each cookie with flaky sea salt. To create the signature button-look, use a wooden toothpick to poke four small holes in the top of each cookie.
8. Let the cookies cool completely before eating (they are crisper when cooled) and store in an air-tight container.