Preheat the oven to 350°F (177°C). Line a sheet pan with parchment paper.

Melt the butter in a medium skillet over medium-low heat. Bring it to a gentle simmer. It will foam up and sputter a little. Cook the butter, swirling the pan often, until it smells nutty and has brown bits at the bottom, about 5 minutes. Immediately pour the brown butter into a medium mixing bowl and let it cool completely.

Once the butter is cool, add 66 grams (⅓ cup) of sugar. Whisk until the mixture is thick and lightened in color, 1-2 minutes. Whisk in the egg yolk and vanilla extract until smooth.

Add the flour, cornstarch, baking soda, cream of tartar, and Kosher salt to the wet ingredients. Use a rubber spatula to fold the cookie dough just until it comes together and there are no more streaks of flour.

Mix the remaining 24 grams (2 tablespoons) of sugar with the cinnamon. Using a #20 cookie scoop, scoop the cookie dough into 6 balls. (The dough will be a little soft.) Carefully roll the cookie dough balls in the cinnamon sugar and place them 2-3 inches apart on the prepared sheet pan.

Bake the cookies for 8-9 minutes, until the edges are set and the centers are still a bit under-done. Let the cookies cool on the sheet pan for 5 minutes. Then, transfer them to a wire rack to cool completely. Enjoy!