For the custard
Preheat the oven to 190°C, 375°F, Gas 5 and grease a 1.1ltr/2pt ovenproof dish.
Remove the crusts from both loaves and cut into slices. Butter the slices and cut each slice diagonally to make 2 triangles. Place a layer of bread triangles, buttered side up, on the base of the ovenproof dish. Combine the dried fruit, lemon zest and juice and the sugar and sprinkle two-thirds of it over the base. Top with more layers of bread triangles until all the bread is used, then scatter over the remaining fruit.
To make the custard, whisk together the eggs, milk, cream, vanilla and mixed spice, if using. Pour the mixture evenly over the bread and dried fruit, taking care to coat the bread in the corners of the dish as well as the centre. Leave to stand for 30 minutes, then lightly press the bread with the back of a fork to ensure it soaks up all the liquid. Bake in the preheated oven for 25-30 minutes until the pudding is golden brown on top.