Heat oven to 350ºF. Line 2 baking sheets with parchment; set aside for one hour.
In a mixing bowl beat butter and granulated sugar together on medium speed until fluffy, about 3 min. Mix in vanilla and egg white. Reduce speed to low and add flour and salt; mix until combined. Wrap dough in plastic and chill overnight.
Pinch off a 1¼-inch ball of dough. Roll into a 5½-inch rope. Shape into a candy cane hook and place on baking sheet; repeat with remaining dough, spacing cookies about 1 inch apart. Bake 12 to 15 min, until cookies are cooked through but not browned. Let cool on parchment on a cooling rack.
In a small bowl thin about ½ cup Lemon Royal Icing with extra lemon juice or water to the consistency of milk. Use a small clean brush to paint entire cookie or paint stripes; sprinkle cookies with sanding sugar and tap off any excuses. Set aside to dry for 1 hr.
Just get these cookies sprinkled with sugar before the icing dries. It dries quickly so I work with one cookie at a time! I use a clean paint brush to paint the stripe of icing (and sprinkle each stripe before I paint the next. (For easier cleanup, I like to sprinkle over a sheet pan with sides to catch the extra.)