Combine flour, salt and ground ginger into a bowl and whisk to combine. Stir in rolled oats.

Using a stand mixer with the paddle attachment beat butter and sugar together on medium speed until light and fluffy, about 5 minutes.

Add dry ingredients and mix just until combined. Fold in candied ginger with a sturdy spatula and divide dough in half. Place each half on a 12 to 14-inch length of parchment paper or waxed paper. Shape the log into a rectangle by flattening the top and sides with your hands. Use the paper to help roll and shape dough into 2 logs, 10 inches in length and roughly 2 inches in diameter.

Twist the ends of the paper to seal the log and chill until firm, at least 2 hours and up to 3 days.

(Logs of shortbread dough can be frozen for up to 3 months.)

Preheat oven to 325°F and line baking sheets with parchment paper. Lightly brush each log with egg white wash. Roll log in turbinado or similarly coarse sugar, using some pressure so that sugar adheres to the dough.

Slice cookies 1/4 to 1/2-inch thick and place 1 inch apart on prepared pans. Bake 16 to 20 minutes, rotating the pan halfway through the baking time. The cookies are done when they begin to brown slightly around the edges and the centers are still light.