Preheat oven to 350°F/180°C and line a baking tray with baking paper and set aside.
In a large bowl, whisk together the sugars and butter.
Whisk in the egg and vanilla, beating until light ribbons fall off the whisk.
Stir in the flour and baking soda and then mix with a spatula.
Fold in the chocolate chunks evenly, then chill the dough for at least 40 minutes. For less spreading, chill the the dough longer.
Roll the cookie dough into balls and place onto the prepared baking tray leaving space between each cookie to allow for spreading.
Bake for 12-15 minutes, or until the edges have started to barely brown.
Notes
The cookies did turn out flatter than I hoped so was a little disappointed with that. I think next time I would chill the dough a bit longer to see if that helped. The cookies were definitely chewy and the use of real chopped chocolate was a definite win.