Weigh all the ingredients. Mix flour with bicarbonate of soda, chop the chocolates into small pieces. Set aside.
Place (on the stove) a small saucepan on medium heat. Cook and swirl or stir occasionally, until the butter starts to foam and turn brown (or golden brown), about 10 minutes. Then immediately pour into a small bowl to cool for about 10 minutes.
In a stand mixer (using a paddle attachment) beat the browned butter, brown sugar and white sugar on medium-high speed for about 3 minutes.
While the mixer is running, add the egg and vanilla extract and beat on medium-high speed until well combined and fluffy, this should take a 1 minute or 2 minutes.
Stop the mixer, add flour mixture, beat until the flour is roughly combined, about 30 seconds, in between sprinkle salt. Add chopped chocolate pieces and beat again for about 30 seconds. Transfer the dough into a medium bowl, refrigerate for 30 minutes and let it rest on the countertop for 30 to 60 minutes.
Meanwhile, preheat the oven to 200℃. Line 2 large baking sheets with baking paper, and set aside.
Using an ice creams scoop, scoop the dough, place 6 to 7 scoops on each prepared baking sheet about 5 to 8cm apart, do not flatten.
Transfer the baking sheet into the preheated oven, and reduce the temperature to 180℃ (from 200℃), then bake for 12 to 15 minutes or until the edges of cookies are lightly golden. I baked mine for 15 minutes.
Let cookies cool on the baking sheets for 10 minutes, then transfer onto wire racks.
Bake the remaining baking sheet for 12 to 15 minutes or until the edges of cookies are lightly golden. Then repeat step 9,