Sieve flour, sugar and salt into a mixing bowl. Rub in softened butter a little bit at a time with the tips of the fingers until mixture resembles fine breadcrumbs. Do this very gently and lightly or mixture will become greasy and heavy. Add just enough iced water to make a good dough. Shape dough lightly into a flattened round, wrap in foil or plastic and put in refrigerator for at least 1 hour to ripen and become firm. If chilled dough is too firm for handling, leave at room temperature until it softens slightly. Then turn out on to a floured board and roll out in usual manner; place in a 9-inch pie tin and press out with fingertips.
Prick with a fork; cover with a piece of foil; fill with dried beans and
Beat cream, milk, clam juice and eggs with a whisk. Place chunks of lobster and prawns on the baked pastry shell. Pour the beaten egg mixture over the lobster and prawns.