How to get the smallest date from a list of objects with a date?

I created a simple class that represents a project:

public class EntityAuftrag
{
    public string cis_auftrag { get; set; }
    public string bezeich { get; set; }
    public DateTime? dStart { get; set; }
    public DateTime? dEnd { get; set; }
    public decimal? aufstunde { get; set; }
    public int id_auftrag { get; set; }
    public string barcolor { get; set; }
}

Now I have a list of these. I want to extract the smallest date, how do I do that?