Heat the clotted cream and milk in a saucepan until nearly boiling.
Whisk egg yolks and caster sugar in a bowl and slowly incorporate the hot cream mixture.
Cook the custard over low heat, stirring constantly until thick enough to coat a spoon.
Sieve the custard, cool completely, churn in an ice-cream machine, and freeze for two hours.
Butter a 1 litre pudding basin and pour in the golden syrup mixed with orange zest and juice.
Cream the butter and brown sugar, then beat in the eggs, black treacle, and flour.
Spoon the batter into the basin and seal tightly with pleated greaseproof paper, foil, and string.
Steam the pudding in a deep pot with water halfway up the basin for two hours.
Turn the pudding out onto a plate and serve with a scoop of ice cream.