Using electric beaters (or a mixer), beat the butter for a minute, then add the icing sugar and beat until incorporated and fluffy, about 1 minute. Beat in the vanilla, then add the flour, cornstarch and salt and beat on low speed. Once incorporated, beat on medium-high speed (or more vigorously by hand) until the dough comes together. Add the Skor bits and stir in.
Shape the dough into 2 logs about 10 inches (25 cm) long (1 1/2-inches/3.5 cm across) and wrap tightly in plastic wrap and chill for at least 2 hours until firm.
Preheat the oven to 325(F (160 (C) and grease or line 2 baking trays with parchment paper.
Unwrap and slice the dough into cookies 1/2-inch (5 mm) thick and arrange them on the baking trays leaving at least 1/4-inch (1 cm) between them. Bake for about 16 minutes, until the cookie barely start to show a little colour at the edges. Cool the cookies completely on the baking tray before removing. The cookies can be stored in an airtight container for up to a week.
More information and baking inspiration is available at www.hersheyskitchens.ca.