Struggling with generic class... design?

public class BaseClass {
  public BaseClass() { /* Constructor */ }
  public static T? JsonDeserialiseAs<T>(string json) where T : BaseClass { /* Do stuff */ }
}

public class MyClassA : BaseClass {
  public string? SomeProp { get; set; } // Some properties that BaseClass doesn't have
  public MyClassA() : base() { /* Constructor */ }
}