In a large bowl, cream the softened unsalted butter, brown sugar, and granulated sugar until light and fluffy.

Add in the large egg yolk and vanilla extract, mixing until everything is fully incorporated.

Gently stir in the all-purpose flour and salt until just combined, ensuring not to overmix.

Carefully fold in the toffee bits and chocolate shavings or mini chocolate chips, if using.

Divide the soft dough into two logs, about 2 inches in diameter. Wrap each log in plastic wrap and chill in the refrigerator for at least 2 hours.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Once chilled, slice the dough into ¼-inch rounds and place them on the prepared baking sheet.

Bake in the preheated oven for 10-12 minutes or until the edges are lightly golden.

Allow the cookies to cool completely on the baking sheet. Drizzle with caramel sauce if desired.