Preheat an oven to 180˚C/ 350˚F and line baking sheets with parchment or baking paper. In a medium sized bowl whisk together the flour, baking soda and salt.
In the bowl of a stand mixer, large mixing bowl with a ladle or using hand held mixer, beat the butter and sugar until creamy and smooth.
Add the egg and vanilla and blend until incorporated. Add the cocoa powder and beat thoroughly till combined. Reducing the mixer speed to low, add the flour mixture. mix till just combined. Do not over mix.
Scoop a tablespoons of dough onto prepared baking sheet leaving enough space for spreading.
Bake in the preheated oven for 10 to 12 minutes or until set on top and no longer looking shining. The cookies will be very soft, allow to cool on the baking sheet for 3 minutes before transferring to a wire rack to cool completely.
Store baked chocolate cookies in an air tight container for up to seven days. Unbaked chocolate cookie dough can be stored in the freezer for up to three months.