Preheat oven to 180oC/350oF/Gas
4. For the base, place the crushed biscuits in a bowl and add the
butter or margarine. Mix to combine.
Press the mixture evenly over the base
and sides of a 23cm / 9in pie dish. Bake for 8 minutes, then cool.
Beat the yolks until thick. Beat in
the milk, lime rind and juice and coloring, if using. Pour into the
pastry case and chill until set, about 4 hours. To serve, whip the
cream. Pipe a lattice pattern on top, or spoon dollops around the edge.