Preheat the oven to 180°C (160°C for fan assisted ovens). Grease an 18cm round loose-bottomed cake tin or spring form tin and line the base with baking paper.
Make up the cheesecake mix as directed on the box with the soft cheese and 1 egg. Fold in the orange zest and set aside.
Make up the brownie mix as directed on the box with the butter, water and remaining egg. Spoon the mixture into the prepared tin and spread evenly. Spoon the cheesecake mix evenly over the brownie batter.
Bake for 35-45 minutes or until the edges are light golden brown. Leave to cool in the tin for 30 minutes then chill in the fridge for 2 hours.
To make the chocolate frosting, place the chocolate, butter and golden syrup in a heatproof bowl set over a pan of simmering water, stirring occasionally until melted and smooth. Remove the bowl from the heat, cool for 5 minutes then stir in the cream to make a smooth glossy frosting. Leave in a cool place for 15-20 minutes, stirring occasionally, until thick enough to spread.
Meanwhile, put the orange strips in a small saucepan with 3 tablespoons cold water. Bring to the boil then simmer for 2-3 minutes until the strips are soft. Drain and refresh under cold water and pat dry with kitchen paper.
Remove the brownie cheesecake from the tin and place on a serving plate. Spread the frosting over the top of the cheesecake, swirling with the tip of a palette knife. Decorate with the orange strips. Chill in the fridge for 20-30 minutes to allow the frosting to firm up slightly before serving.