Preheat oven to 325° F. Line two baking sheets with parchment paper.
In a large bowl, using a hand mixer (or stand mixer), mix melted butter, brown sugar and granulated sugar until well creamed.
Add in egg, egg yolk and vanilla extract. Mix until lighter in color.
Add in the flour, baking soda and salt and mix again. Scrape the sides of the bowl and the bottom really well to ensure a smooth, well stirred batter.
Hand stir the chocolate chunks into the batter and let it sit 20 minutes to let the flour soak into the rest of the batter. (If your oven tends to run hot - aka flattens cookies - refrigerate the dough for 20 minutes.)
Scoop cookie dough onto prepared pans, using a two tablespoon cookie scoop.
Bake 8-9 minutes, rotating sheets halfway through baking. When you pull your cookies out of the oven, they will looked cooked around the edges and undercooked in the center. DO NOT OVERBAKE!!
Carefully place a few chocolate chunks on top of each cookie immediately after removing from oven, pressing into the warm soft cookie just slightly.
Leave the cookies on the hot baking pans for 5-7 minutes or until you can remove them without falling apart. Place onto cooling racks and cool to room temperature before storing in air tight containers.