In a small saucepan heat the milk, over a low heat, along with 1/2 cup of the cream, the caster sugar, and half the zest until sugar dissolves, about 5 minutes. Do not boil. Remove from heat and allow cool.
Beat the egg yolks in a bowl with the cooled milk mixture until combined. Pour into a small saucepan and cook over low heat, stirring constantly with a wooden spoon, until the mixture thickens to a custard like consistency. Be careful not to let the mixture get too hot or the eggs will cook. Strain, and add remaining mandarin zest.
Add the mandarin juice and the lemon juice to the mixture. Whisk together and chill. Pour into an ice-cream maker and freeze according to manufacturer's instructions.