In a large mixing bowl, beat the soft butter with an electric mixer for 1 minute or until smooth. Add the powdered sugar, brown sugar, vanilla and salt. Blend on medium until combined. Scrape down the sides and bottom of the bowl with a rubber spatula, and blend again.

Add the flour in forths, mixing on low speed after each addintion until incorporated. The dough will seem a little dry, but keep mixing as it comes together.

Add the chopped chocolate to the cookie dough and carefully mix in using a wooden spoon, or mix in using your hands.

Place the dough on a large piece of parchment paper. Form the dough into a 12 inches long log. Wrap the dough tightly in the parchment paper and refrigerate for at least 4 hours or overnight.

To bake preheat oven to 350 degrees. Line two baking sheets with parchment paper, set aside.

Remove the dough from the refrigerator. Using a large, thin, sharp knife, slice the log into 24 (1/2-inch) rounds. I use my bench scraper.

Place the cookies on the prepared cookies sheets, about 1-inch apart. Sprinkle the tops of each cookie with sea salt, if desired.

Bake at 350 degrees for 16-20 minutes or until the they are starting to brown on the bottom and the cookies are set. Cool on a wire rack and store in an airtight container.