Mix the dry ingredients. Combine the flour and salt in a bowl; whisk to blend and set aside.

Combine the sugar and zest. In a small bowl, combine the granulated sugar, orange zest, lemon zest, and cardamom; use a spoon to mash the zest into the sugar to combine it thoroughly. Stir in the cardamom. Set aside.

Cream the butter and sugar. In a mixing bowl with an electric mixer, beat the butter until smooth and creamy. Add the sugar and zest mixture and the confectioners' sugar and beat until fluffy, about 3 minutes.

Finish the dough. Add the egg yolk to the creamed mixture and beat until well combined. Refrigerate the egg white until it's time to cut and bake the cookies. Add the flour mixture and mix on low speed just until blended.

Shape and chill the dough. Shape the dough into 2 equal logs about 8 or 9 inches in length. Wrap the logs in plastic wrap and refrigerate for at least 2 hours.

Prepare the oven and pan. When it's time to bake, heat the oven to 350°F and line cookie sheets with parchment paper.

Apply the egg wash. Whisk the egg white and brush over a cookie dough roll and then roll in sparkling sugar or a large-grain sugar.

Slice and bake. Cut a roll into 1/2-inch slices and place them 1 1/2 inches apart on the prepared cookie sheet. Repeat with the remaining roll of cookie dough. Bake the sablés until lightly browned on the bottoms, about 18 to 20 minutes.

Cool and store. Cool the cookies in the pan for 5 minutes then move them to a rack to cool completely. Store sablés in an airtight container for up to 1 week, or freeze in a resealable freezer bag or container for up to 6 months.