Preheat the oven to 180°C, fan 160°C, gas 4. Butter the bread on one side. Spread the mincemeat on to the bread, then cut into triangles and arrange in a 2-litre ovenproof dish. Tuck the pears between the slices.
Beat together the caster sugar, milk, double cream and the eggs. Strain and then pour over the bread and pears. Sprinkle over the demerara sugar and allow to stand for 20 minutes. Bake for 30-35 minutes or until the custard is just set.
Allow to stand for a further 15 minutes, then serve with a drizzle of fresh cream, if you're feeling indulgent.