In a medium bowl, sift together the both flours, salt, baking soda and corn startch then set aside.
1 cup bread flour, 1 cup all purpose flour, 1/2 tsp salt, 1 tsp baking soda, 2 tsp corn starch
In a stand mixer bowl add in the room temperature butter, both sugars and cream together until light and fluffy. This will take a couple of minutes. If you don't have a stand mixed, you could use an electric hand mixer and mix for about 1-2 minutes.
1 cup unsalted butter, 1 cup brown sugar, 1/3 cup granulated sugar
Add in the egg and the egg yolk, vanilla extract, and espresso powder and beat just until incorporated.
2 tsp vanilla extract, 2 tsp espresso powder, 1 egg, 1 egg yolk
Add in the dry ingredients and gently fold using a spatula just until the flour disappears. Don't worry about the unmixed flour on the edge of the bowl, it will get incorporated in whenever we mix the chocolate chips in.
Add in the semisweet chocolate chips/chunks and the chopped up dark chocolate bar and fold until the chocolate is evenly distributed.
3/4 cup good quality semi sweet chocolate chips, 2 oz dark chocolate bar
Using a #16 scoop (about 4 tbsp), scoop out the cookie dough into a parchment or silpat-lined baking sheet, top with more chocolate chunks for that bakery-style finish. Cover the baking sheet with plastic wrap and let the cookies sit in the fridge for two hours. If you are going for optimal flavor here, let the cookie sit in the fridge overnight. This will allow them to develop a deeper flavor!
When the cookies are ready to be baked, preheat the oven to 350F. Transfer the cookie doughs to a different parchment lined baking sheet, making sure to leave at least 3 inches between each cookie. These cookies will spread so we don't want them to get stuck together,
Bake in the preheated oven for 12 minutes. The cookies might still look raw in the center but don't worry about that. They will continue cooking as they cook.
As soon as your cookies come out of the oven, you can shape them using a large cookie cutter. Place the cutter around the cookie and gently swirl the cookie around to round it up and keep it at that perfect thickness. Sprinkle with flakey sea salt.
flaky sea salt for topping
Let the cookies cool on the baking sheet for 5-10 minutes before transferring them to a cooling wrack to cool completely.