Combine the dry ingredients

• Whisk the flour, cornstarch, baking soda and salt together in a bowl.
• Set the dry mixture aside.

Melt the butter

• Melt the butter and let it cool slightly.
• Melted butter gives the cookies their chewy, fudgy texture.

Whisk the wet ingredients

• Whisk the melted butter with the brown sugar and granulated sugar.
• Whisk in the egg, extra egg yolk and vanilla until combined.
• No mixer is required.

Make the dough

• Combine the wet and dry ingredients until a soft dough forms.
• Fold in the chocolate chips.

Chill the dough

• Cover and refrigerate the dough for at least 2 hours, preferably overnight.
• Chilling prevents excess spreading.

Shape the cookies

• Measure about 60 g of dough per cookie.
• Shape into tall, lumpy columns rather than smooth spheres.

Bake

• Arrange the dough on a baking tray and bake at 180 °C until the edges are set and the centers still soft.
• Press a few extra chocolate chips into the warm cookies.