Melt butter in pan and mix with crushed cookie; press into pie plate. In a sauce pan, stir together sugar, corn starch, zest, lemon juice and water. Cook until thickened. Add a little of the hot mixture to the yolk to temper. Add back into pan and cook 1 more minute. Pour mixture into the pie crust and chill. Meanwhile, whip the egg white and sugar to stiff peaks. Top pie with meringue and torch.