Process the ricotta and sugar in a food processor until smooth.
Finely chop the nougat or wrap in a tea-towel and smash with a rolling pin until broken into small pieces.
Whip the cream until soft peaks form. Combine the ricotta mixture, nougat, cream and zests in a bowl and mix well. Pour into a 2-liter mold that has been rinsed in cold water. Freeze until set. Turn out onto a platter and serve cut into slices with lime slices or fresh seasonal fruits.
Recipe courtesy Everyday Epicurean by Catherine Bell (Ten Speed Press, 2000); Photograph by Kieran Scott