Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given an integer array nums where the largest integer is unique.
Determine whether the largest element in the array is at least twice as much as every other number in the array. If it is, return the index of the largest element, or return -1 otherwise.
 
Please complete the following python code precisely:
```python
class Solution:
    def dominantIndex(self, nums: List[int]) -> int:
```