In a large mixing bowl, beat unsalted butter with granulated sugar and brown sugar using an electric mixer on medium speed for 2-3 minutes until light and fluffy.

Add egg yolk and vanilla extract to the mixture, mixing on low speed until fully combined.

In a separate bowl, whisk together flour and a pinch of salt. Gradually incorporate this into the wet mixture on low speed until just combined.

Fold in the chocolate chips and toffee bits gently with a spatula, ensuring even distribution.

Divide the dough into two portions and shape into 2-inch logs. Wrap in plastic wrap and chill in the refrigerator for at least 2 hours.

Preheat oven to 350°F (175°C). Slice chilled logs into 1/2-inch rounds and place on a lined baking sheet. Bake for 12-15 minutes until edges are golden.

Cool on a wire rack for 5 minutes before transferring to cool completely. Store in an airtight container.