Combine the milk and cream in a saucepan and bring to a boil.
Beat the egg yolks with the sugar and pour the hot liquid over them, stirring constantly.
Return the mixture to the saucepan and cook, stirring, over low heat until the custard coats a metal spoon. Do not allow the mixture to boil.
Soak the gelatin in the rum and dissolve it in the hot custard. Cool, stirring occasionally, until the custard is thick and begins to set. Pour it into a mold rinsed in ice water. Chill for several hours or overnight. Unmold by loosening the edges with a knife and dipping the bottom of the mold quickly into hot water.