Pour the milk into a small saucepan and stir in the ground almonds. Bring to the boil, then set aside.
Put the egg and the yolk into a heatproof bowl with the sugar and beat until pale and thick. Pour on the milk and almond mixture. Place the bowl over a pan of gently simmering water and stir until thick. Stir in the almond essence and leave to cool.
Purée the cherries in a food processor or blender (or use cherry compôte), then stir into the custard.
Toss the slivered almonds in a heavy pan over a low heat to toast them. Leave to cool.
Whip the cream until it forms soft peaks. Fold the whipped cream into the cherry mixture.
Transfer the mixture to a freezer container, cover and freeze until firm, beating twice at hourly intervals. Stir the slivered almonds into the mixture at the last beating. (If using an ice-cream machine, pour the cherry mixture into the machine, add the cream, churn and freeze. Once frozen, fold through the slivered almonds.) Serve the ice cream in individual glasses.