Cartesian product by pattern matching

I'm a student at the university and am learning Scala. I've got an exercise which is to make cartesian product using pattern matching and not using any operations on list.

def find[A,B](aList: List[A], bList: List[B]): Set[(A,B)] = {
  def findHelper[A,B](aList: List[A], bList: List[B], acc: Set[(A,B)]): Set[(A,B)] = {
    (aList, bList) match {
      case (head1 :: tail1, head2::tail2) => {
        findHelper[A, B](tail1, tail2, acc ++ Set((head1, head2)))
      }
      case (List(), head2::tail2) => acc
      case (List(), List()) => acc
    }
  }
  findHelper(aList, bList, Set())
}
println(find(List(1,2,3,4,5), List(7,8,9,10,11)))

As a result I get only like (1,7), (2,8) etc. I obviously know why, but I don't know how to combine each pair with itself. I don't know what to do, when my first list gets empty after :: operation.