Cook the peeled chestnuts until soft and press them through a potato press. Separate the eggs and beat the yolks with the powdered sugar and lemon zest over a water bath until the mixture begins to thicken. Add the chestnut puree and mix well. Beat the egg white and the cream separately until stiff and fold into the dessert mixture one after the other. Soak gelatine sheets, squeeze out and dissolve in the heated rum. Also pull under the mass. Fill into buttered dessert molds and let set in the refrigerator for several hours.
To serve, turn out the molds and serve the cream with a fruit sauce.
The cream dissolves easily if you briefly put the molds in hot water.