Make the compôte. Put the blueberries and half the sugar into a small pan, place over a low heat and cook for 4–5 minutes until the berries are softened and beginning to ooze their juices. Set aside while you make the toasts.
Beat together the egg, cream or milk and cinnamon in a shallow bowl. Dip the brioches into the egg mixture and soak well.
Heat the butter in a nonstick frying pan, add the brioche and cook over a medium heat for 3–4 minutes, turning occasionally until browned all over. Serve with the blueberry compôte.