When you take the butter out of the refrigerator to make the cookie dough, take out 1/2 cup more (1 stick) and allow to soften as you make the cookies. This softened butter is for the frosting.

Toss the flour, cream of tartar, baking soda, cinnamon and salt together in a large bowl. Set aside.

In a medium bowl, whisk the melted butter, granulated sugar and brown sugar together until smooth. You must use a whisk in order to prevent the butter from separating from the sugars. Whisk in the egg, then the vanilla until combined. Pour the wet ingredients into the dry ingredients and mix together with a large spoon or silicone spatula. The dough will be very thick and heavy, yet slightly crumbly. Cover the dough tightly with plastic wrap and chill for at least 45 minutes and up to 2 days. (If chilling for longer than a few hours, be sure to let the cookie dough sit at room temperature for 20-30 minutes because it will be quite hard.)

Preheat oven to 350°F (177°C). Line two large cookie sheets with parchment paper or silicone baking mats. Set aside. Remove the cookie dough from the refrigerator and roll 1.5 Tablespoons of dough into each ball. I like to use this medium cookie scoop. You’ll have about 20-24 balls, give or take.

Mix the sugar and spices together in a small bowl. Roll each dough ball into the mixture to coat evenly. Place 10 balls of dough onto each cookie sheet. Bake the cookies for 10-11 minutes. The cookies will look very puffy, soft, and under baked. That’s ok. Remove from the oven and allow to cool on the cookie sheet for at least 10 minutes before transferring to a wire rack to cool completely.

(frosting is optional): With a handheld or stand mixer fitted with a paddle attachment, beat the butter on medium speed until creamy—about 2 minutes. Add confectioners’ sugar, vanilla extract, cream, and vanilla bean seeds with the mixer running on low. Increase to high speed and beat for 3 full minutes. Add 1 Tablespoon more cream if frosting is too thick. Taste and add 1/8 teaspoon salt if frosting is too sweet. I always add the salt.

Frost cooled cookies. There may be leftover frosting depending how much you use on each cookie. Sprinkle with extra sugar/chai spice topping if you have any left, if desired. Cookies stay fresh covered at room temperature for 1 week.