Melt the butter and mix the sugars

• Melt the butter and let it cool slightly.
• Whisk the melted butter with the brown sugar and caster sugar until smooth and glossy.

Add the eggs and vanilla

• Whisk in the egg, egg yolk and vanilla extract until fully combined and slightly pale.

Fold in the dry ingredients

• Add the plain flour, cornflour, bicarbonate of soda and salt.
• Fold with a spatula until just combined, with no dry streaks left.

Add the chocolate

• Fold in the chopped Kinder bars and white chocolate chunks, keeping a little back for the tops.

Chill the dough

• Divide the dough into 8 large balls and place on a lined tray.
• Chill in the fridge to firm up.

Bake the cookies

• Preheat the oven to 200 °C.
• Space the dough balls well apart on lined baking trays and press the reserved chocolate on top.
• Bake until the edges are set and golden but the centres still look soft.

Cool and serve

• Leave the cookies on the tray to firm up slightly, then enjoy while still gooey in the middle.