Preheat the oven to 180 C / Gas 4. Grease a 20cm springform cake tin and line the edge with a strip of baking parchment (cut taller than the side of tin to allow for a 'collar').
In a large mixing bowl, beat together the butter and the sugar until pale and fluffy. Beat in the eggs, one at a time, until the mixture is smooth. Sift in the flour then add the ground almonds and mix well. Finally mix in the orange zest and Cointreau® and stir until smooth. Transfer to the prepared cake tin and smooth the top.
Bake in the oven for 45 minutes until golden then cover with aluminium foil and cook for a further 15 minutes until a skewer inserted into the centre comes out clean. Remove from the oven, remove the foil and allow to cool fully in the tin.
For the topping:
In a frying pan over a medium heat, melt the sugar then add the orange slice and cook for 4 to 6 minutes on each side or until golden brown and caramelised. Remove from the pan and set aside.
Pour the cream into a saucepan over a high heat and bring almost to the boil. Remove immediately from the heat and stir in the chocolate until melted. Allow to cool (but not so much that it is setting) then pour the chocolate over the cooled cake. When the chocolate has firmed up a little add the caramelised orange slice.
Once the chocolate is fully set, pop the cake out of the springform tin and peel away the baking parchment leaving a smooth outside edge. Decorate with grated chocolate. Slice and serve.