Combine milk, cardamom pods and 6 Tbsp of the sugar in a saucepan. Bring to boil, turn to low and stir in rice. Continure stirring until sugar dissolves. Cover and cook over a very low heat for 1 hour. Remove from heat.
Put egg yolk in a cup and beat lightly. Add 2 Tbsp hot pudding to the cup and mix slowly. Pour mixture back into the pan and stir through.
Stir in remaining sugar. Bring to a simmer and cook, stirring every so often until pudding is thickened, about 5 to 7 minutes. Remove and discard cardamom pods. Add sultanas and half the slivered almonds. Mix well and let cool completely.
Whip cream until stiff. Reserve 3 Tbsp and fold in rest into cooled rice pudding. Transfer to a 1/5 litre gratin dish. Sprinkle remaining almonds on top.
Preheat grill (broiler) to maximum and place pudding under it briefly until lightly browned. Leave to cool and refrigerate until ready to serve.