Whisk butter and sugars

• Whisk the melted butter with the granulated sugar and light brown sugar until the mixture looks like wet sand.

Add egg and vanilla

• Add the egg and vanilla extract.
• Whisk until fully combined.

Sift in the dry ingredients

• Sift the flour, baking soda and salt into the bowl.
• Fold until almost combined.

Fold in the chocolate

• Fold in the dark chocolate chips and milk chocolate chips until evenly distributed.

Scoop and chill the dough

• Scoop the dough into 9 to 11 portions.
• Chill in the fridge for at least 1 hour or overnight.

Preheat the oven

• Preheat the oven to 180 °C (350 °F).

Shape and bake

• Roll the chilled dough into balls and place them on a lined tray, 2 inches apart.
• Bake for 9 to 12 minutes until the edges are set; underbake for chewy cookies.

Cool the cookies

• Cool on the tray for 5 to 10 minutes.
• Transfer to a rack to cool completely.