public class TestController : ApiController
{
    // This method must be synchronous
    public void Test()
    {
        Debug.WriteLine($"Main Thread {Thread.CurrentThread.ManagedThreadId}");
        // I must use a Task here because otherwise I will have to block async code which will cause a deadlock
        var task = Task.Run(() =>
        {
            Debug.WriteLine($"Child Thread {Thread.CurrentThread.ManagedThreadId}");
            SomeAsynchronousWork().GetAwaiter().GetResult();
        });
        task.GetAwaiter().GetResult();
    }

    public async Task SomeAsynchronousWork()
    {
       // some work that must be done asynchronously
    }
}

Main Thread 5
Child Thread 5