Sieve the raspberry puree to remove any seeds if this hasn’t already been done. Put the double cream and sugar into a saucepan and bring to the boil. Remove from the heat and stir in the raspberry puree and lemon juice. Leave to cool slightly.
When the mixture is cool, carefully pour it into 6 wine glasses and chill until set, which should take about 2 hours.
Then make the biscotti
Pre-heat the oven to 180c. Tip all the ingredients, except the eggs, into an electric mixer and mix together. Add the eggs and blend to form a stiff dough.
Remove the dough and shape it into 2 large, flat logs about 30cm long and 12cm wide and 2.5cm high. Lay them on a large baking sheet and bake for 20 minutes or until the logs are cooked throughout but not too brown. When they are cool enough to handle, lift the logs on to a board and slice very thinly (about 5mm thick) on an extreme diagonal, then place the separate biscuits on 1 or 2 baking sheets. Bake for another 10 minutes or until pale golden brown and crisp. You should make about 25-30 biscotti. Serve the possets with the biscuits.