Preheat the oven to 350°F. Line a baking sheet with parchment paper.
Whip the butter and sugar. Beat the softened butter and 1⅓ cups cane sugar on high for about 2 minutes, or until lighter in color and creamy. Scrape down the sides and bottom of the bowl.
1 cup unsalted butter,1⅓ cups granulated cane sugar
Add the remaining wet ingredients. Mix in the egg, extra egg yolk, and vanilla until fully combined.
1 large egg,1 large egg yolk,1 tbsp vanilla extract
Add the dry ingredients. With the mixer on low, gradually add the flour, arrowroot, baking soda and salt. Mix just until combined, scraping the bowl as needed.
2¾ cups einkorn flour,2 tsp arrowroot,1 tsp baking soda,½ tsp salt
Portion and coat. Place the remaining 1/4 cup cane sugar in a small bowl. Use one level #30 scoop of dough per cookie, or roughly 2 tablespoons. Gently roll into balls, then roll in the sugar. Place about 3 inches apart on the prepared baking sheet. If the dough is too soft to handle, refrigerate until scoopable.
1/4 cup granulated cane sugar
Bake or freeze. Bake immediately, or place the dough balls on a lined tray and freeze until firm. Once frozen, transfer them to a freezer-safe container or bag.
Bake fresh dough for 8–10 minutes or frozen dough for 10–12 minutes, without thawing. The cookies are ready when the edges are lightly golden and set, while the centers still look slightly soft.
Let the cookies cool on the baking sheet for about 5 minutes before transferring them to a cooling rack. Enjoy!