Adjust an oven rack to the middle position. Line 2 baking sheets with parchment paper
In a small bowl, whisk the flour, baking soda and salt.
In the bowl of a stand mixer fitted with a paddle, beat the butter on medium until creamy about 1 minute. Add the granulated and brown sugars and beat on medium until light and fluffy, 2 to 3 minutes. Add the egg, vanilla and 2 tablespoons water, and mix on low to combine. Add the flour mixture, and mix on low until combined. Add the chocolate and mix on low into the batter. (At this point, the dough can be refrigerated for several hours or overnight.)
Heat the oven to 350 degrees. Form the dough into 2.5 ounce (~70 gram) balls (#24 ice cream scoop 1/3 cup each). Place 4-5 balls an equal distance apart on pan.
Place the baking sheet in the oven and bake 7 minutes, until the cookies are puffed slightly in the center. Lift the baking sheet and let it drop down against the oven rack, so the edges of the cookies set and the inside falls back down. (This will feel wrong, but trust me.) Bang it down, if necessary, to make the center fall.
After the cookies puff up again, 2 minutes later, repeat lifting and dropping the pan. Repeat a few more times, every 2 minutes, to create ridges around the edge of the cookie. Bake 13 to 14 minutes total, until the cookies have spread out, and the edges are golden brown, but the centers are much lighter and not fully cooked.
Transfer the baking sheet to a wire rack and sprinkle with Fleur de sel or Maldon salt. Let cool10-15 minutes before removing the cookies from the pan.
Repeat with remaining cookies. Store in an airtight container.