Cut the vanilla pods in half lengthwise and scrape out the pulp.
Bring the milk to the boil with the vanilla pulp and pod, remove from the heat. Whip the egg yolks with the sugar over a hot water bath until creamy, pour the vanilla milk through a sieve and whip until creamy. Allow to cool. Add the mocha powder and vanilla ice cream to the cooled vanilla sauce and mix vigorously to make a smooth sauce.
