Preheat the oven to 180°C/350°F/gas 4. Peel, core and slice the apples and put them in a pan with the caster sugar and 30 g/ 1 oz of the unsalted butter. Add 3 tablespoons of water, cover the pan and stew gently over a low heat for 10 minutes. Then remove the lid, stir and turn up the heat, continuing to cook until you have a thick purée. Stir in the lemon juice and apricot jam, and reserve.
Melt the remaining butter and cut the crusts off the slices of white bread. Cut them into fingers, brush with the butter and use them to line a 20-cm / 8-inch mould or soufflé dish. Pour and spoon in the purée and cover the top neatly with more butter-soaked bread.
Bake on a baking sheet in the oven for 35 minutes, when the top will be crisp and golden-brown. Remove and leave to cool for 10 minutes, before sliding a palette knife round the edge and turning out on a serving dish.
Cut into wedges and serve with clotted cream, whipped cream or vanilla ice-cream. Do not serve immediately it comes from the oven as the apple filling will be incandescent.