In a large bowl, whisk together the sugars, salt, and butter until a paste forms with no lumps.
Whisk in the egg and vanilla, beating until light ribbons fall off the whisk and remain for a short while before dissolving back into the mixture.
Sift in the flour and baking soda, then fold with a spatula to combine. (Be careful not to overmix, as the gluten in the flour to toughen resulting in cakier cookies.)
Fold in the chocolate chunks.
Chill the dough for at least 30 minutes or, for a more intense, toffee-like flavor and deeper color, chill overnight. The longer the dough rests, the more complex its flavor will be.
Preheat the oven to 350°F (180°C). Line a baking sheet with parchment paper.
Scoop the dough with an ice-cream scoop onto the prepared baking sheet, leaving at least 4 inches (10 centimeters) of space between cookies and 2 inches (5 centimeters) of space from the edges of the pan so that the cookies can spread evenly.
Bake for 12–15 minutes, or until the edges have started to barely brown.
Let the cookies cool completely, then dunk in the melted chocolate. Let chocolate set for about 30 minutes.