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

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 the butter is almost fully melted (25 sec for room temp butter, 40 sec for fridge cold butter on high).

Whisk to finish melting the butter.

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.

Add 1 cup chocolate chips, stir to disperse and flour is fully incorporated. Batter will be quite loose.

Stand for 5 minutes for batter to firm up a bit so it is scoop-able into mounds.

For large cookies: Scoop up a level ice cream scoop / 3 tablespoon / ¼ cup and place on baking trays 5cm / 2" apart - 13 balls. Top with remaining choc chips.

For small cookies: Scoop up 1.5 tablespoon or ½ an ice cream scoop, place on baking trays 4cm / 1.75" apart, top with choc chips.

Bake 1 tray at a time. Large cookies: Bake for 8 minutes, rotate the tray and bake for 3 minutes. Small cookies: Bake 6 minutes, turn then bake 3 minutes.

Cool on the tray as they finish cooking.