Preheat the oven to 350° F.
Whisk the dry ingredients- all purpose flour, bread flour, baking soda, baking powder, cornstarch and salt in a medium bowl and set aside.
In a stand mixer using the paddle attachment (or a bowl with a hand mixer), beat the butter for about 3-5 minutes, until light and fluffy.
Add the granulated sugar and brown sugar, and vanilla extract. Continue mixing for another 2ish minutes, scraping down the sides of the bowl.
Add in the egg and egg yolk. Mix until combined.
Add the dry ingredients to the mixer a little at a time and mix together until fully incorporated, about 30 seconds. Fold the chopped chocolate, along with the chocolate chips and chopped toffee in the cookie dough.
Chill the dough for about 30 minutes.
Scoop cookie dough onto a parchment paper-lined sheet tray with a standard cookie scoop.
Bake for about 10-12 minutes, then allow to finish baking on the hot cookie sheet for about 2ish minutes.
Top with extra chocolate chips and toffee pieces while the cookies are still warm.Transfer to a wired rack. Enjoy!