Step 1

Line a baking sheet with parchment paper and set aside

Step 2

In a small heavy sauce pan over low heat bring the butter and sugar to a boil, stirring occasionally. Bring the mixture to 285°F on a candy thermometer, the mixture will become a deep amber color. Immediately remove the pan from the heat, cool for 1 minute and spread the mixture evenly onto the prepared pan. Allow the toffee to cool completely and then using a knife, break it into small pieces.

Step 3

In the bowl of your stand mixer fitted with the paddle attachment beat the butter and both sugars together for 2 minutes. Add in the egg, yolk, vanilla, corn syrup, baking soda, salt and cornstarch. Mix for 1 minute on medium, or until the mixture is evenly combined.

Step 4

Turn the mixer to low and add in the flour, mixing until just combined.

Step 5

Stir the toffee bits into the cookie dough and chill for 1 hour.

Step 6

Preheat the oven to 325°F and line a baking sheet with parchment paper.

Step 7

Using a medium (2 tablespoon) cookie scoop drop the dough onto the lined baking sheet 3 inches apart. The cookie will spread while baking.

Step 8

Bake for 11-13 minutes until the cookies are golden brown at the edges.

Step 9

Allow the cookies to cool on the pan for 5 minutes and then transfer them to a wire rack to cool completely.