1cupsalted European style butter~85% fat butter, see recipe note #1
1/4cupdemerara sugar55g, see recipe note #2
Sift flour, baking powder and salt into a medium bowl. Set aside.
In a stand mixer fitted with the paddle attachment, cream butter and sugar until light and fluffy, about 3 minutes. Add egg yolk and mix until combined. Add dry ingredients and mix until combined.
Shape dough into a ball and transfer to a lightly floured work surface (see recipe note #3). Divide dough in half with bench scraper or sharp knife. Roll each half into a 1 1/2-inch diameter log. Brush off excess flour.
Sprinkle demerara sugar onto a sheet of parchment paper. Roll each dough log in sugar until well coated. Wrap each log tightly in plastic wrap and refrigerate for 1 hour or more.
When you're ready to bake the cookies, preheat oven to 325˚F and line 2 baking sheets with parchment paper.
Slice each dough log into 1/4-inch thick rounds and place on prepared baking sheets at least 1-inch apart. Bake 18 minutes or until golden brown on the bottom and edges. Remove from oven and let cool slightly (about 5 minutes) before transferring to cooling rack.
Store cooled cookies in an airtight container at room temperature.
European Style Butter or cultured butter is a higher fat butter vs. many in the US, look for 85% butterfat. There are many foreign and domestic brands that make this style of butter. If you are using unsalted butter, increase the sea salt to 1/2 teaspoon.
Demerara sugar is a coarse sugar that is less refined than standard brown sugar.
A lightly floured work surface keeps the dough from sticking as you roll it into a log, but makes it difficult for the demerara sugar to adhere. Brushing off the flour before you roll in sugar is helpful. For maximum sugar adhesion, don't flour your work surface and work quickly to roll the logs to keep the dough from sticking to the work surface.
The dough logs freeze beautifully! You can slice and bake the logs straight from the freezer, no thawing required. Just add a minute or so to the baking time.
Note that the baking time is per batch of cookies.