1/4-1/3cupsparkling or granulated sugar(50-66 grams)
In the bowl of the mixer cream the butter on medium speed, then add the sugars and salt, beat for one minute. Reduce the speed to low then add the egg yolks and vanilla beat for one minute. Be sure to scrape the bowl.
Continue on low speed and add the flour in three additions, combining as you add.
Mix the dough just until combined, the dough will be soft. There may be flour remaining at the bottom of the bowl, mix it into the dough with a spatula.
Place the dough on a lightly floured flat surface and knead gently into a ball. Divide the dough into two parts. I formed one into a log about 8-9 inches (20-22 cm) and one into a ball. The log is for slice and bake and the round is for cut out cookies. You can do the same or do one or the other. (If you make of the same type of cookie, be sure to make either two logs or two rounds for easier handling of the dough). Wrap the dough in plastic and chill for at least three hours.
Remove the dough from the fridge. Brush the log with the egg wash (in a small bowl beat together the egg and milk), then sprinkle it with sparkling sugar, cut into 1/3" slices and place on a parchment paper lined cookie sheet.
To make the cut-out cookies, roll the dough on a lightly floured flat surface and cut out with your favourite cookie cutters. Place the cut outs on a parchment paper lined cookie sheet and sprinkle with sparkling sugar or granulated sugar. No egg wash needed.
Refrigerate the cookies again while the oven is pre-heating at 325F (160C).
Once the oven is ready remove the cookies, one sheet at a time from the fridge and bake 15-17 minutes or until the cookies are light brown on the bottom and lightly golden around the edges but still pale on top.
After 2-3 minutes carefully remove the cookies with a metal spatula from the cookie sheet and carefully place on a wire rack to cool completely. Enjoy!