Preheat oven to 350°F (180°C) (standard) or 320°F (160°C) (fan / convection). Place oven shelf in the middle.

Line 2 trays with baking / parchment paper.

Whisk the flour, salt, and baking soda in a bowl.

Place the butter in a large heatproof bowl. Microwave until almost fully melted (25 sec for room temp butter, 40 sec for fridge cold butter on high).

Whisk to finish melting the butter completely.

Add brown and white sugar, whisk energetically for 15 seconds.

Add egg, yolk, and vanilla, whisk well for 15 seconds.

Add flour mixture and mix until flour is almost fully incorporated.

Fold in chocolate chips until just combined.