Place all ingredients in a food processor and pulse till the butter and flours are mixed and become a crumbly texture.
Place the dough onto a sheet of cling wrap.
Wrap the dough with cling wrap and shape the dough into a long cylinder shape 1.5 inch/4cm in diameter. *5
Roll the cookie dough with a bamboo sushi mat and rest the dough in fridge at least 1 hour. *6
Start to preheat the oven to 374°F/190°C. *7
After the dough is rested at least one hour in fridge, remove the cling wrap and roll the dough on the granulated sugar. *8 step by step photo no9.
Slice the cookie dough 0.2inch/5mm thick. *9
Lay the sliced cookie dough on a silicone mat placed oven tray and bake in 356°F/180°C , middle rack for about 18 minutes. *10
Cool cookies on a cooling rack.
With Stand Mixer
Soften the butter in room temperature in a mixing bowl of a stand mixer.
Add sugar and beat with whisking attachment.
Add egg into the bowl and mix in three different times. *11
Sift and add the flour into the bowl. Change the attachment to the beater attachment and combine the cookie dough.
From this point same as the food processor process.
Notes
*1 choose a flour that contains around 7 % of protein. *2 If you are unable to get vanilla powder, it can be replaced with 1 tsp of vanilla essence. *3 A pinch of salt is the salt pinched with a thumb, index and middle fingers. *4 Softening butter is unnecessary. All ingredients need to be cold in order to avoid too much gluten forming. *5 Divide the dough into two equal portion cylinders. I made and took photos with half of the amount. *6 Rolling with a sushi mat is to rest the dough in vertical position as the step by step photo no. 8 indicates. If you don't have one, you can shape the cookie dough square instead and lay vertical in fridge. Also if possible, rest the cookie dough overnight for a better result. *7 When the chilled ingredients are placed inside the oven, oven temperature will drop, therefore needs to be preheated at a slightly higher temperature. *8 granulated sugar is not listed in the ingredients. *9 Photo showing only 18 cookies because I made them with half the amount of the ingredients for the photos. *10 This baking time is an indication only. Everyone's oven is different, so you may need to adjust the baking time. *11 So that the egg and butter does not separate. *Nutritional fact is for 1 cookie.
If you don't have both food processor, use the stand mixer process and manually beat and combine ingredients.