How can I send a cookie from a Web.Api controller method

I have a Web.Api service which has a method that accepts a custom class and returns another custom class:

public class TestController : ApiController
{
    public CustomResponse Post([FromBody]CustomRequest request)
    {
        // process request
        ...
        // create response
        CustomResponse resp = new CustomResponse() { ... };
        return resp;
    }
}

Now I want to also send a cookie back as part of the Http response. How can I do that?