Cream together butter and sugars. Add in the egg and beat it until the mixture is light and fluffy.
Combine together the rest of the dry ingredients together (flour, black sesame powder, baking soda, salt and cream of tartar) and fold it into butter mixture.
Line a medium-sized tray (jelly roll pan size) or plate with plastic wrap. Using an ice-cream scooper or spoon, divide the cookies out into 12 equal sized balls and place them in the tray. Cover the top with plastic wrap and refrigerate the cookies for at least 1 hour.
Preheat the oven to 350F. Prepare your cookie sheet.
Remove the cookies from the fridge and let it rest at room temperature for 10 minutes. In the meantime, combine turbinado sugar and toasted black sesame seeds* together in about a 2:1 ratio. After the cookie dough has rested, roll them in the sugar mixture and place it on the cookie sheet about 4 inches apart.
Bake in the oven for 15 minutes, or when the edges have browned and the top has set. About 7 minutes into the bake, lift the baking sheet a few inches off the rack in the oven and drop it. Do this 3 times. This will create ripples in the cookie and cause it to spread. Rotate the pan and let it bake for another 3 minutes before repeat this dropping.
Let cool for about 5-10 minutes on the baking sheet before transferring it to a cooling rack. Enjoy!