In a bowl, combine flour, baking soda and salt. Set aside.

In another bowl, mix melted butter, brown sugar, sugar and vanila until well combined and thick in texture.

Pour flour mixture, stir with spatula until well combine then add sourdough starter and egg yolk. Eventually add assorted choco chips. Mix well.

Scoop dough into a small balls or shape it manually (mine was 30gr each). Place in a parchment lined baking tray with some space in between.

Bake at temperature 180 degC for about 10-15 minutes. Add some minutes in case you prefer a hardened cookies. Cool completely in a cooling rack.

Enjoy!