Chop the pistachios very finely. Peel grapefruits so that the white skin is completely removed. Use a sharp knife to cut out the fillets between the parting skins and fill them into jars until some are ready for decoration. Mix egg yolk, sugar and white wine in a bowl, beat in a hot water bath until thick and creamy.
Fold in rum and ground pistachios, up to 1 teaspoon. Fill the zabaglione onto the grapefruit fillets. Pour the rest of the fillets onto the cream. Sprinkle with pistachios
Table linen: ASA