• Combine the cold butter and powdered sugar in the large bowl of a stand mixer and beat until smooth and creamy, scraping down the sides of the bowl as needed.
  1 cup salted butter, 2/3 cup powdered sugar
• Mix in the vanilla and salt, then slowly add the flour on low speed, mixing just until the dough comes together.  
  1 1/2 teaspoons vanilla extract, 1/4 teaspoon salt, 2 cups all-purpose flour
• Stir in the toffee bits and chopped pecans, then divide the dough into two even-sized portions and shaped into logs that are each 6 1/2-inches long and approximately 1 1/2 to 1 3/4-inches in diameter. I find it's easiest to squeeze the dough tightly to compress and make sure there aren't any air pockets in the center, then roll it out on a lightly floured surface until it's the right size.
  3/4 cup toffee bits, 1/2 cup finely chopped pecans
• Wrap each log tightly in plastic wrap and refrigerate for 1 hour until chilled.
• Heat oven to 350°F before removing the shortbread dough from the fridge.  Line a baking sheet with parchment paper, then slice each log into 14-15 slices, each slightly less than 1/2-inch wide. Arrange the sliced shortbread dough on the prepared baking sheet, then bake for 12-16 minutes, until just barely turning golden brown around the edges.  
• Remove from oven and cool completely on a wire rack.  

Chocolate Dipping

• If you choose to dip the cooled toffee pecan shortbread cookies in chocolate, melt the chocolate in a microwave-safe bowl for 20 seconds at a time on the defrost setting, stirring between each burst of heat, until completely melted.
  10 ounces dark chocolate
• Dip half of each cookie in the chocolate, then shake off the extra and lay flat on a parchment-lined baking sheet. Sprinkle with additional toffee bits or chopped pecans before the chocolate has a chance to set, then allow the chocolate to set completely for about an hour at room temperature or in the refrigerator for quicker results.  
• Store in an airtight container for up to 5 days at room temperature. These cookies also freeze very well.