How to create a custom response base in Angular HTTP service?

Question

I am returning a custom response from Spring Boot API as below:

public static ResponseEntity<Object> generateResponse(String message, HttpStatus status, Object responseObj) {
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("Message", message);
        map.put("Status", status.value());
        map.put("Output", responseObj);

        return new ResponseEntity<Object>(map,status);
    }

which it will return: message, status and the output. So now I am wondering how could I make a custom response in Angular to receive all these three attributes. How should I replace the "???" with? I should be customizing the response base right?

public Get(): Observable<Book>{
    return this.http.get< ???<Book> >(this.baseUrl).pipe(map(response => response.Output))
  }