In a large bowl, cream together butter, brown sugar, and granulated sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

In a separate bowl, whisk together flour, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Fold in the toffee bits evenly.

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

Preheat oven to 350°F (175°C). Slice dough into 1/4-inch rounds.

Place slices on a parchment-lined baking sheet and bake for 10–12 minutes or until edges are golden.

Cool on baking sheet for a few minutes before transferring to wire racks.