Soak the gelatine in cold water. Heat the cream and milk in a pan until just starting to simmer.
Stir in the white chocolate and the sugar. Remove the pan from the heat then stir in the soaked and drained gelatine until completely dissolved. Divide between 4 dariole moulds or dishes of your choice and set aside in the fridge to set for at least 4 hours.
Hull and halve the strawberries. Heat the champagne in another saucepan. Pour the boiling champagne over the strawberries then leave to cool.
Melt the dark chocolate in the microwave and spread it to an even thickness over a tray lined with baking paper. Scatter with the chopped toasted nuts and place the chocolate slab in the fridge to cool.
Remove the chocolate slab whilst still slightly soft. Cut into triangles large enough to hold a panna cotta. Return the chocolate triangles to the fridge to set completely.
Turn the panna cotta out onto the chocolate triangles by warming the moulds slightly. Serve with a bowl of the champagne soaked strawberries. Serves 4