Preheat the oven to 190°C. Peel the pears, cut them in half, then scoop out the seeds and core. Place them in a baking tray (facing downwards), then brush each with the lemon juice.
Put the sugar, cinnamon and butter in a pan, then gently simmer over low heat until you get a thick, smooth sauce. Don't boil it!
Glaze the pears with the sauce, then bake for 20-25 minutes until golden, brushing them with more syrup several times during this time.
Serve with custard or ice cream, garnished with thin lemon peel slices.