Preheat the oven to 180°C/160°C fan and butter the baking dish (approx. 26 x 19 x 6 cm).
Coarsely grate or thinly slice the peeled and cored apples.
Heat the milk in a pot until quite warm but not too hot.
Whisk the eggs with vanilla in a large bowl.
Pour the warm milk over the beaten eggs and keep whisking until the ingredients are properly combined.
To assemble the pudding:
Cut the brioche into 12 slices (the pudding has 3 brioche layers - 4 slices per layer)Tip: You can cut the brioche slices in half or quarters or squash them into place to make them cover the whole surface.
Dip the first 4 slices in the warm milk and arrange them over the base of the buttered baking dish.
Spread half of the apples over the first brioche layer. Sprinkle them with ½ the amount of sugar and ½ teaspoon of cinnamon.
Repeat the process by dipping 4 brioche slices in the milk and layer them on top of the apple filling, covering the entire area.
Spread the remaining apples across the second brioche layer; sprinkle them with the remaining sugar and ½ teaspoon of cinnamon.
Dip the last 4 brioche slices in the milk and lay them on top of the apples. These slices make the top layer of the pudding.
Place a generous slice of butter on each brioche and pour any remaining milk over the pudding.
Bake at 180°C/160°C fan for approximately 50 minutes or until the pudding is nicely golden brown.
Serve it while the pudding is still warm, or let it cool down to room temperature.