In the bowl of an electric mixer fitted with a paddle attachment, over medium/high speed, beat butter and sugars for about 2-3 minutes until combined. To the sugar/butter mixture add the egg, egg yolk, vanilla bean paste, corn syrup, baking soda, kosher salt, and cornstarch. Mix on medium speed until the mixture is well combined. Stop and scrape the mixer.
Add in the flour at once. Turn the speed to very low and mix until just combined. You should still see some flour bits. Remove bowl from mixer. Fold in the toffee pieces, making sure to scrape the bottom of the mixer to ensure the dough is fully incorporated with the toffee pieces.
Cover the mixer bowl with plastic wrap. Place the bowl in the fridge and chill the dough for at least 35-40 minutes.
Preheat the oven to 325° Fahrenheit and line two baking sheets with parchment paper.
Using a medium cookie scoop, scoop cookie dough into your hands and roll quickly. Place the balls of cookie dough onto the baking sheet at least 2 ½ inches apart. Flatten the dough slightly.
Place in the oven and bake for at least 11 minutes until the edges are golden brown and the toffee has melted. Don’t worry, the toffee will solidify.
Remove pans from the oven. Allow the cookies to cool on the pan for 5 minutes and then transfer them to a wire rack to cool completely.
Makes about 3 dozen cookies.
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