Line your baking sheets with parchment paper and preheat your oven to 350°F (175°C).
Mix Wet Ingredients In a large bowl, combine the melted butter with both brown and white sugars. Whisk until the mixture is smooth and the sugars are well incorporated. Add the eggs one at a time, mixing well after each addition. Pour in the milk and vanilla extract, then whisk until the mixture is smooth and slightly lighter in color.
Combine Dry Ingredients In a separate bowl, whisk together the flour, salt, baking soda, baking powder, and cornstarch. This ensures even distribution of the leavening agents throughout the dough.
Gradually add the dry ingredients to the wet mixture, stirring just until combined. Fold in the chocolate chips and chopped chocolate bar pieces, reserving some for topping the cookies.
Fold in the chocolate chips and chopped chocolate bar pieces, reserving some for topping the cookies.
chill the dough for at least 30 minutes, or ideally overnight. This allows the flour to hydrate properly and the flavors to develop fully.
Scoop chilled dough using a 3-tablespoon cookie scoop onto the prepared baking sheets, leaving ample space between each cookie. Press additional chocolate pieces onto the tops of the cookie dough balls.
Bake for 7-9 minutes, or until the edges are lightly golden but the centers still look slightly underbaked.