The stock has to be hot going in — that's the whole thing, and it's why home risotto goes gluey. Adding cold stock drops the pan temperature and the rice releases starch unevenly. Chef Emily kept a second pan on the heat throughout and made everyone do the same. The other useful point was stopping while it still looks slightly too loose, because it keeps thickening off the heat. Mine was creamy rather than stodgy for the first time.
Hugo