class BaseClass
{
    public string PropertyA { get; set; }
}

class DerivedClass: BaseClass
{
    public string PropertyB { get; set; }
}

class ContainerClass
{
    public DerivedClass ComplexProperty { get; set; }
    public string PropertyC { get; set; }
}

class SourceClass
{
    public string PropertyA { get; set; }
    public string PropertyB { get; set; }
    public string PropertyC { get; set; }
}

Mapper.CreateMap<SourceClass, ContainerClass>()
    .ForMember(d => d.ComplexProperty, o => o.MapFrom(s => Mapper.Map<DerivedClass>(s)))
    .AfterMap((s, d) => System.Diagnostics.Debug.WriteLine("SourceClass-> ContainerClass mapped"));

Mapper.CreateMap<SourceClass, DerivedClass>()
    .AfterMap((s, d) => System.Diagnostics.Debug.WriteLine("SourceClass -> DerivedClass mapped"));

Mapper.CreateMap<BaseClass, DerivedClass>()
    .AfterMap((s, d) => System.Diagnostics.Debug.WriteLine("BaseClass -> DerivedClass mapped"));

var source = new SourceClass {
    PropertyA = "ValueA",
    PropertyB = "ValueB",
    PropertyC = "ValueC",
};

var destination = Mapper.Map<ContainerClass>(source);

Console.WriteLine("PropertyA: " + destination?.ComplexProperty?.PropertyA);
Console.WriteLine("PropertyB: " + destination?.ComplexProperty?.PropertyB);
Console.WriteLine("PropertyC: " + destination?.PropertyC);

PropertyA: ValueA
PropertyB:
PropertyC: ValueC

SourceClass -> DerivedClass mapped
BaseClass -> DerivedClass mapped
SourceClass -> ContainerClass mapped