Preheat your oven to 350°F (175°C).
In a medium bowl, whisk together the flour, baking soda, cornstarch, and salt.
In a large mixing bowl, beat the softened butter and brown sugar together until light and fluffy.
Add the egg and vanilla extract to the butter and sugar mixture and beat until well combined.
Gradually add the dry ingredients to the wet mixture and stir gently until just combined.
Fold in the chocolate chips and toffee pieces, ensuring they are evenly distributed.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 10-12 minutes or until the edges are golden brown.
Cool on the baking sheet for 5 minutes, then transfer to a cooling rack.
