In a large bowl with an electric mixer, beat the softened butter, powdered sugar, and vanilla extract on medium-high speed until light and fluffy, about 2-3 minutes.

In a separate medium bowl, whisk together the all-purpose flour and kosher salt.

With the mixer on low, gradually add the flour mixture to the butter mixture. Mix until just combined. Do not overmix.

Using a spatula, gently fold in the chopped dark chocolate chunks until evenly distributed throughout the dough.

Turn the dough out onto a piece of parchment paper and form it into a log approximately 2 inches in diameter. Roll the log tightly in the parchment paper and twist the ends to seal. Chill in the refrigerator for at least 2 hours, or until very firm.

Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper. Remove the chilled dough log and slice it into 1/2-inch thick rounds.

Place the cookie slices on the prepared baking sheets, about 1 inch apart. Bake for 12-15 minutes, or until the edges are just beginning to turn a light golden brown.

Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.