Implement an Interface with Generic Methods

You should rework your interface, like so:

public interface IOurTemplate<T, U>
        where T : class
        where U : class
{
    IEnumerable<T> List();
    T Get(U id);
}

Then, you can implement it as a generic class:

public class OurClass<T,U> : IOurTemplate<T,U>
        where T : class
        where U : class
{
    IEnumerable<T> List()
    {
        yield return default(T); // put implementation here
    }

    T Get(U id)
    {

        return default(T); // put implementation here
    }
}

Or, you can implement it concretely:

public class OurClass : IOurTemplate<string,MyClass>
{
    IEnumerable<string> List()
    {
        yield return "Some String"; // put implementation here
    }

    string Get(MyClass id)
    {

        return id.Name; // put implementation here
    }
}