Preparation: Align three oven racks and preheat to 180°C (350°F) for optimal cookie baking environment.

Butter Transformation: Using an electric mixer with paddle attachment, cream butter until smooth. Gradually add granulated and light brown sugars, whipping until light and fluffy.

Moisture Integration: Blend egg, vanilla extract, and warm water at low speed until just combined, creating a uniform wet mixture.

Dry Ingredient Fusion: Whisk all-purpose flour, baking soda, and kosher salt together, ensuring even distribution of dry ingredients.

Dough Development: Merge dry ingredients into butter mixture at low speed. Fold in bittersweet chocolate, including fine chocolate fragments, using a spatula to create a cohesive dough.

Portioning and Chilling: Scoop 12 uniform dough portions using a 2¼-inch ice cream scoop. Freeze for 15 minutes to enhance cookie structure.

Initial Baking Cycle: Position 4 dough balls on parchment-lined trays with ample spacing. Bake for 10 minutes until centers slightly rise.

Texture Manipulation: Remove trays and tap against stovetop to deflate cookie centers. Return to oven, repeating tapping every 3 minutes for 18-20 minutes, achieving golden-brown edges and soft, pale centers.

Finishing Touch: Rotate trays during baking for even browning. Once complete, sprinkle fleur de sel or sea salt across cookies and cool entirely on baking trays.