In a double boiler, on a gentle heat, whisk egg yolks and castor sugar until thick and glossy.
Once ready, place pot in cold water and allow to cool, whisking occasionally.
While cooling, place the cherries, sugar and liqueur (optional) in a saucepan and heat until the sugar melts and cherries become sticky.
When zabaglione (egg and castor sugar mix) is cool, fold cream into the mixture.
To serve: Toast raisin bread, top each slice with zabaglione and cherries, and serve hot.