Mix the butter and sugars

• Put the melted butter, caster sugar and light brown sugar in a bowl.
• Stir until well combined.

Add the egg yolk

• Add the egg yolk and mix until smooth.

Fold in the dry ingredients

• Add the heat-treated flour, salt and chocolate chips.
• Fold gently until just combined, without overmixing so the cookie stays soft.

Fill the mug

• Spoon half of the cookie dough into a mug.
• Press the Lindor ball into the centre.
• Cover with the remaining dough and top with a few chocolate chips.

Microwave

• Microwave on high (750 W). If your microwave is much more powerful, use medium-high or check the cookie at 50 seconds.

Serve

• Let it cool for a moment and enjoy warm, while the centre is still gooey.