- Pick over and wash the sloes, then place in a pan and just cover with water.
- Bring to the boil and simmer gently on the stove until the sloes break down and become pulpy.
- Drain and rub through a sieve into a clean pan.
- Discard the stones, reheat the sloes and sweeten to taste with caster sugar.
- Leave to cool.
- Butter a 2-litre pudding basin and place a disc of baking parchment in the bottom.
- Mix 2 heaped tablespoons of the sloes with the blackberry jam.
- Spoon the mixture into the base of the basin and smooth up the sides a little.
- Cream the butter and sugar together until pale and fluffy.
- Beat in the eggs a little at a time, then add the gin.
- Sieve the flour and salt together and fold into the butter and egg mixture.
- The mixture should be of a dropping consistency: if it's a little dry mix in a little milk to slacken it.
- Spoon on top of the jam in the basin and level off with a spatula.
- Cover with a disc of buttered parchment, then with pleated foil and steam for 1½ - 2 hours.
- When cooked, turn onto a serving plate and leave to stand for a few minutes before unmoulding.
- Serve with sweetened whipped cream.