Preheat your oven to 350°F (175°C) to ensure even baking and perfect texture.
Line a baking sheet with parchment paper to prevent sticking and for easy cleanup.
In a medium bowl, whisk together the all-purpose flour, cocoa powder, and baking soda. Set aside.
In a large mixing bowl, use an electric mixer to beat the room temperature butter, light brown sugar, and granulated sugar together until light and fluffy, about 2-3 minutes.
Mix in the vanilla extract and fleur de sel (or fine sea salt) into the creamed butter and sugar mixture until fully incorporated.
Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; the dough should be soft and slightly crumbly.
Using a cookie scoop or a tablespoon, portion out the dough and place it onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 12-15 minutes or until the edges are firm but the centers are still soft.
Remove from the oven and allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack. While they are still warm, sprinkle a touch more fleur de sel on top for extra flavor.
Once cooled, enjoy your delicious salted chocolate shortbread cookies with your favorite beverage.