Chewy Dark Chocolate Chunk Pistachio Cookies

1 In a large bowl, mix the softened butter, brown sugar, and granulated sugar until smooth and creamy. Make sure the butter is soft to the touch, not melted, so it blends properly and gives the cookies the right texture.
2 Add the egg yolks and vanilla extract, then mix until fully combined and smooth.
3 In a separate bowl, whisk together the flour, cornstarch, baking soda, and salt until evenly combined.
4 Add the dry ingredients to the wet ingredients and mix until just combined. Stop mixing as soon as you no longer see dry flour so the cookies stay soft.
5 Fold in the chocolate chunks and pistachios until evenly distributed throughout the dough.
6 Cover the dough and refrigerate for 30 to 45 minutes to help control spreading.
0 Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.
7 Scoop about 3 tablespoons of dough per cookie and place them on the prepared baking sheets, leaving space between each one. Press a few extra pieces of chopped chocolate on top of each dough ball so you get melted chocolate pools on the surface after baking.
8 Bake for 11 to 13 minutes, until the edges are set and the centers still look slightly soft. Do not overbake, as this is what keeps the cookies gooey in the center.
9 Let the cookies cool completely on the baking sheet.