Mix together flour and salt.
Using food processor grind candy canes to fine sugar consistency.
Using electric mixer, beat butter, sugar, and candy cane sugar together until fluffy (about 4-5 minutes)
Add eggs, egg yolk and vanilla, beat to combine.
Add flour a bit at a time until all the flour is combined.
Separate into 2 or 3 even pieces, wrap in plastic wrap and chill in refrigerator for at least 30 minutes.
Preheat oven to 350º F. Line baking sheets with parchment paper.
Flour work surface, then roll dough to 1/4 inch thickness.
Dust cookie cutters with flour before cutting shapes from dough.
Transfer to baking sheet. Place baking sheet into refrigerator for 10 minutes to chill the dough again. This will prevent cookies from spreading so they keep the nice sharp edges.
Bake 350ºF for 8-10 minutes (just until edges start to brown)
Cool completely. Decorate with royal icing.