How to convert List of Lists to a 2D array in C#

Dear all,
As you can see, I take reference to create the function to take points on surface by uv


As illustrated in Dynamo:

You can see that the result is a nested list of lists and even you can acess one item like vars[n][m] in Dynamo.
So my question is, how to convert List of Lists to a 2D array in C#( or directly form a 2D array without using list of list) so that I can access one item of the list like Points[n][m] for extra operation?