In a large bowl, beat butter and maple sugar with an electric mixer on medium speed until creamy and smooth

Beat in yolk until fully incorporated

In a medium bowl, whisk flour, baking powder and salt

Add flour mixture to butter mixture and beat for about 20 seconds, until a smooth dough comes together

Pat dough on the counter to form a 1x2x7 inch brick

Wrap in plastic and refrigerate dough for at least 4 hours, until completely chilled

Preheat oven to 375 degrees F

Use a sharp knife to cut half the dough into ¼ inch slices

Refrigerate remaining dough

Arrange slices on the baking sheet, spacing them generously

Sprinkle with turbinado sugar, if using, per cookie

Bake for 8-10 minutes, until lightly browned

Remove from the oven and cool on baking sheet for 5 minutes before transferring cookies to a cooling rack to cool completely

Repeat with remaining dough