1. Put all the ingredients for the base into a food processor or liquidiser and process until smooth.

2. Pour the mixture into an 1 8cm / 7" greased spring mould or flan tin lined with foil and bake at 350°F/180 °C/gas mark 4 for 45 minutes until just set.

3. Leave in the tin to cool before removing.

4. To make the frosting, mix the margarine, milk, lemon juice and zest together before gradually adding the icing sugar.

5. Colour carefully with a little food colouring.

6. Roll into balls about 1.2cm / 1/2" in diameter, arrange over the base and fork down to make a pattern.

7. Chill for at least 2 hours before serving.