Divide the kumquats lengthwise into 4, place in a saucepan with the water and sugar, bring to a boil, simmer for half an hour at a low temperature. Cool.
(This can be done one or more days before: it is even better if the kumquats marinate in the sugar syrup for a while after boiling ! ).
Bring condensed milk to a boil, remove from heat, add chocolate while stirring and let it melt, perfume with Grand Marnier.
(Can also be prepared in advance).
Chestnut ice cream
Pass the chestnut puree through a sieve, add the condensed milk, mix well, perfume with Grand Marnier, add the chocolate cubes. Whip cream until stiff, stir in gently. Place in a mold (about 17 to 18 cm long) and freeze (not in an ice cream maker, just in the freezer !).
Defrost ice cream a little, cut into slices . Warm chocolate sauce, spread evenly on plates and arrange ice cream on top. Garnish with kumquats.
Bring the remaining sauce to the table separately.
The candied kumquats can of course also be eaten without ice cream!
Tip: Feel free to use better chocolate – the more delicious the result!