Pre-heat the oven to 180°C/350°F/gas 4 and grease a
Roll out the pastry and use to line the flan tin or ring. Line the pastry with greaseproof paper, fill with baking beans and bake blind in the pre-heated oven for 20 minutes. Remove the beans and paper, trim round the top of the ring and leave to cool.
To make the filling, mix the milk, cream, sugar and butter in a pan and bring to the boil. Gradually whisk in the polenta and semolina, lemon zest and juice and salt, being careful to avoid any lumps. Transfer to a bowl and sit the bowl over a pan of hot water. Cook the mix for 20 minutes, stirring frequently, until the mix is very thick. Stir in the sultanas and rum. If the mix is too thick and slightly stodgy then simply thin down with a little more milk or cream. Pour the mix into the flan case, cover with buttered greaseproof paper to prevent a skin forming and leave to cool. The flan should not be turned out until completely set.
This eats very well on its own or with cream. As an alternative, some apple wedges cooked in butter and sugar can be placed on top, sprinkled with icing sugar and glazed under a hot grill.