Preheat your oven to 350 degrees
In a large bowl, combine 1 cup of room temperature butter with 3/4 cup of brown sugar and 2/3 cup of granulated sugar
Using an electric hand mixer, mix on medium speed until fully combined
Add 2 large eggs and 2 teaspoons of vanilla extract and mix until light and fluffy
Place a mesh sifter over the bowl and add 1/3 cup of natural unsweetened cocoa powder, 1 cup of all purpose flour, 1 cup of bread flour, 1 teaspoon of baking soda, 2 teaspoons of cornstarch and 1/2 teaspoon of salt into the sifter
Gently sift the dry ingredients into the bowl
Mix until the dry ingredients are just combined
Add 1 1/3 cups of dark chocolate chunks and fold to evenly distribute throughout the cookie dough
Add 2 tablespoons of dough onto parchment lined baking sheets about 2 inches apart
Use the back of a grease teaspoon to form indents into the top and fill each indent with softened peanut butter
Bake the cookies in a 350 degree oven for 9-11 minutes or until the edges of the cookies feel lightly set
Transfer the cookies onto a cooling rack or cutting board to cool for about 5 minutes before transferring the cookies directly onto the cooling rack
Sprinkle the warm cookies with flaky sea salt and finely chopped chocolate (optional)
Store leftovers in an airtight container at room temperature