Fluent API design with immutable type. From https://dotnettutorials.net/lesson/fluent-interface-design-pattern/

Employee.cs

using System;

namespace FluentInterfaceDesignPattern
{
    class Program
    {
        static void Main(string[] args)
        {
            var obj = EmployeeExtensions.CreateEmployee(default, default, default, default);
            obj = obj.NameOfTheEmployee("Anurag Mohanty")
                    .Born("10/10/1992")
                    .WorkingOn("IT")
                    .StaysAt("Mumbai-India");

            Console.WriteLine($"Name: {obj.FullName} DOB: {obj.DateOfBirth} Department: {obj.Department} Address: {obj.Address}");

            Console.Read();
        }
    }
    public interface IEmployee
    {
         string FullName { get; }
         DateTime DateOfBirth { get; }
         string Department { get;  }
         string Address { get; }
    }

    internal class EmployeeRecord : IEmployee
    {
        public string FullName { get; }
        public DateTime DateOfBirth { get; }
        public string Department { get; }
        public string Address { get; }

        public EmployeeRecord(
            string fullName,
            DateTime dateOfBirth,
            string department,
            string address
            )
        {
            FullName = fullName;
            DateOfBirth = dateOfBirth;
            Department = department;
            Address = address;
        }
    }

    public static class EmployeeExtensions
    {
        public static IEmployee CreateEmployee(string fullName,
            DateTime dateOfBirth,
            string department,
            string address) => new EmployeeRecord(fullName, dateOfBirth, department, address);

        public static IEmployee NameOfTheEmployee(this IEmployee employee, string fullName) => CreateEmployee(fullName, employee.DateOfBirth, employee.Department, employee.Address);

        public static IEmployee Born(this IEmployee employee, string dateOfBirth) => CreateEmployee(employee.FullName, Convert.ToDateTime(dateOfBirth), employee.Department, employee.Address);

        public static IEmployee WorkingOn(this IEmployee employee, string department) => CreateEmployee(employee.FullName, employee.DateOfBirth, department, employee.Address);

        public static IEmployee StaysAt(this IEmployee employee, string address) => CreateEmployee(employee.FullName, employee.DateOfBirth, employee.Department, address);
    }
}