Cream butter and sugar with a hand mixer or in the bowl of an electric mixer fitted with the paddle attachment. Mix in vanilla, salt, and slowly add in flour. Mix until combined.
Cover a cutting board with a large piece of wax paper. Place the dough in the center, press it down flat, and cover it with another piece of wax paper. Roll the dough into a rectangle (about 8”x10”) between the two pieces of wax paper. Chill for at least 10 minutes.
Place your candy canes in a quart-sized ziploc bag. Roll with a rolling pin to crush. (Careful, the bag will get tiny holes from the sharp candy canes. It’s best to roll it on a cutting board or cookie sheet to minimize mess.)
Line a cookie sheet with more wax paper. Melt white candy according to package directions. Pour half on the prepared cookie sheet and spread it into a rectangle slightly larger than the dough rectangle.
Place the cookie dough rectangle on top of the white candy. Pour the remaining white candy on top and spread to cover, making sure to meet the edges of the bottom layer to seal the dough inside. Sprinkle with crushed candy canes.
Chill until set, at least 30 minutes. Instead of breaking, I have better success cutting this bark into wedges so that the chocolate doesn’t come off the cookie dough. Store in an airtight container in the refrigerator for up to 4 days or freeze for up to one month. Serve at room temperature.