Pre-heat the oven to 200c / 180c fan.
Add the milk and butter to a medium saucepan, and heat gently until the butter is completely melted.
Remove from the heat and set aside.
In a heatproof mixing jug, whisk the sugar, eggs, cinnamon, and vanilla.
Add a splash of the warm milk mixture and whisk thoroughly.
Add a little more milk and whisk again, repeating until everything is well incorporated.
Grease a suitably sized baking dish with some more unsalted butter; I used a 26cm rectangular stoneware dish with a 2.3 litre capacity.
Core the pears, and cut them into neat slices, then layer the bread and fruit into the dish, as attractively as you can.
Carefully pour over the custard mixture, then sprinkle the pudding with some demerara sugar.
Bake for 30 minutes, until golden brown and set.