Make the cookie dough
1-Place the unsalted butter in a microwave: Place the unsalted butter in a microwave safe bowl. Microwave for 30-40 seconds until the butter has melted.
2-Mix in the caster sugar and light: Mix in the caster sugar and light brown sugar until combined.
3-Mix in the vanilla extract, whole egg: Mix in the vanilla extract, whole egg and egg yolk until combined.
4-Fold in the flour to make a: Fold in the flour to make a smooth cookie dough.
5-Add the Kinder Chocolate chunks (save a: Add the Kinder Chocolate chunks (save a handful for later) and fold into the cookie dough.
6-Cover the bowl with clingfilm and refrigerate: Cover the bowl with clingfilm and refrigerate for at least 4 hours or overnight for best results.

Roll and bake the cookies
7-Preheat the oven to 180°C (fan) and: Preheat the oven to 180°C (fan) and line two large flat baking trays with greaseproof paper.
8-Take the cookie dough out of the: Take the cookie dough out of the fridge and leave to soften at room temperature for 30 minutes.
9-Scoop a heaped tablespoon of cookie dough: Scoop a heaped tablespoon of cookie dough and use your hands to roll it into a ball. Place on the baking tray and do not flatten. Repeat this step until all the cookie dough has been used up. Remember to leave roughly 8-10cm between each ball so they have enough room to spread out.
10-Bake for 10-12 minutes: Bake for 10-12 minutes. The cookies should be golden on the edges but the middle still soft, pale and under-baked.
11-As soon as the cookies are out: As soon as the cookies are out of the oven, push a few chunks of Kinder Chocolate into the top of each cookie.
12-Leave on the baking tray for 15: Leave on the baking tray for 15 minutes to cool down and firm up. This will change the cookie texture so resist the temptation to tuck in straight away!