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 four additions and mix on low speed until incorporated. The dough will seem a little dry, but keep mixing.

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

Place the dough on a large piece of parchment paper. Form the dough into a log 14-inches long and about 1 1/2-inches thick. Wrap the dough tightly in the parchment paper and refrigerate for at least 4 hours or up to 4 days.

To bake preheat oven to 350 degrees F.

Line two baking sheets with parchment paper, set aside. Remove the dough from the refrigerator while preparing the egg wash. Whisk together the egg and water. Lightly brush the entire log with the egg wash. Pour some of the coarse sugar down the middle of a piece of parchment or wax paper. Roll the dough log in the sugar to coat, pressing down firmly to adhere until completely coated. Using a large, thin, sharp knife, slice the log into 28 (1/2-inch) rounds. Place the cookies on the prepared cookie sheets, about 1-inch apart. Bake for 12-16 minutes or until the they just start to brown on the bottom. Cool on a wire rack and store in an airtight container.