Preheat the oven
to 180C/350F /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.