Preheat oven to 160°C/140°C fan-forced. Grease a 6cm-deep, 20cm (base) round cake pan. Line base and side with baking paper.

Place chocolate chips from packet mix in a microwave-safe bowl. Microwave on medium (50%) for 1 minute, stirring every 30 seconds with a metal spoon, or until smooth.

Place cake mix in a large bowl. Add eggs, oil and 1 1/4 cups cold water. Stir with a wooden spoon until combined (mixture may be lumpy). Stir in melted chocolate and hazelnut meal.

Pour mixture into prepared pan. Bake for 1 hour 15 minutes or until a skewer inserted in the centre comes out clean. Cool completely in pan.

Make icing following packet directions, using butter and milk. Spread over top and side of cake. Arrange chocolate halves around top of cake. Serve.