Calculate Fibonacci by using parallel tasks and aggregate exceptions. I did it for the cookie.

ExceptionalFibonacciCalculator.cs

using System;
using System.Threading.Tasks;

namespace Fib
{
    class ExceptionalFibonacciCalculator
    {
        public int Calculate(uint n)
        {
            try
            {
                Fibonacci(n).Wait();
            }
            catch (AggregateException e)
            {
                return e.Flatten().InnerExceptions.Count;
            }
            throw new InvalidOperationException("Should never hit this");
        }

        static Task Fibonacci(uint n)
        {
            return n <= 1
                ? Task.Factory.StartNew(
                    () => { throw new Exception(); },
                    TaskCreationOptions.AttachedToParent)
                : Task.WhenAll(
                    Task.Factory.StartNew(
                        () => Fibonacci(n - 1),
                        TaskCreationOptions.AttachedToParent),
                    Task.Factory.StartNew(
                        () => Fibonacci(n - 2),
                        TaskCreationOptions.AttachedToParent));
        }
    }
}

Program.cs

using System;

namespace Fib
{
    class Program
    {
        static void Main()
        {
            var fib = new ExceptionalFibonacciCalculator();
            for (uint n = 0; n < 25; n++)
            {
                var result = fib.Calculate(n);
                Console.WriteLine("Fibonacci({0})={1}", n, result);
            }
        }
    }
}