Step 1

Adjust an oven rack to the middle of the oven. Preheat the oven to 350F [180C]. Line three sheet pans with aluminum foil, dull-side up.

Step 2

In a small bowl, whisk together the flour, baking soda, salt, and cream of tartar.

Step 3

In the bowl of a stand mixer fitted with a paddle, beat the butter on medium speed until creamy, about 1 minute. Add 1 1/2 cups [300 g] of the sugar and beat on medium speed until light and fluffy, 2 to 3 minutes. Add the egg and vanilla and mix on low speed to combine. Add the flour and mix on low speed until combined.

Step 4

Form the dough into 3 oz [85 g] balls [1/4 cup]. Roll each ball in the remaining 1/4 cup [50 g] of sugar. Place 3 or 4 cookies an equal distance apart on the sheet pan. Bake the cookies one pan at a time. Bake until the dough balls have flattened but are puffed slightly in the center, 8 minutes. Lift one side of the sheet pan up about 4 in [10 cm] and gently let it drop down against the oven rack, so the edges of the cookies are set and the center falls back down. After the cookies puff up again in 2 minutes, repeat lifting and dropping the pan. Repeat a few more times to create ridges around the edges of the cookie. Bake for 14 to 15 minutes total, until the cookies have spread out and the edges are golden brown but the centers are much lighter and not fully cooked.

Step 5

Transfer the pan to a wire rack. Let the cookies cool for 10 minutes, then move them to a wire rack to finish cooling. Store cookies in an airtight container at room temperature for 2 days (or refrigerate for up to 3 days).