1tablespoonBob's Red Mill Egg Replacermixed with 2 tbsp water
For the buttercream frosting:
½cup (113g)unsalted butterroom temperature
1 ½cups (180g)powdered sugarsifted
To make the cookies:
In a medium bowl, whisk the flour, arrowroot, baking powder, and salt together. Set aside.
Using a hand mixer or a stand mixer fitted with the paddle attachment, cream the butter with both sugars until smooth. Add the Greek yogurt, prepared egg replacer, and vanilla extract and beat to combine. Add the dry ingredients and mix on low speed until soft cookie dough forms. Cover and chill in the refrigerator for at least 1 hour.
Preheat the oven to 375°F. Line baking sheets with parchment paper. Scoop out cookie dough, measuring about 2 tablespoons per cookie, and roll into a ball. Flatten slightly with your hands. Arrange on the lined baking sheets, 2 inches apart. Bake 8-9 minutes, or until edges look slightly browned. Allow cookies to cool on the baking sheets for 15 minutes before transferring to a cooling rack to cool completely.
To make the buttercream frosting:
Using a hand mixer or a stand mixer fitted with the paddle attachment, beat the butter until smooth and creamy. Add the powdered sugar, milk, and vanilla extract and beat until combined. Pipe or spread frosting on cooled cookies and immediately top with sprinkles, if using.
Cornstarch can be used instead of arrowroot as a 1:1 substitute.
Be sure to follow the instructions on the package of Bob's Red Mill Egg Replacer. Once mixed with water, the egg replacer must sit for just a few minutes to thicken.
If you are not looking to replace eggs, you should be able to use 1 egg instead of the egg replacer.