Preheat the oven to 200 degrees Celsius. Heat the milk in a saucepan and, with a pinch of salt, allow the millet to swell over a small flame for about 30 minutes, then allow to cool. In the meantime, remove the seeds from the South Tyrolean apples and dice them or grate them roughly. Remove from the heat and allow to cool.
Separate the eggs and beat the honey with the egg yolks until frothy. Stir the lemon zest, the chopped nuts and the cooled millet gruel into the egg yolk mixture. Beat the egg whites until stiff and fold them in.
Pour half of the mixture into a baking dish greased with butter, then spread the South Tyrolean apples on top. Sprinkle with cinnamon. Then spread the remaining mixture on top. Finally, spread the butter over the mixture in the form of flakes and bake the casserole in the oven for about 45 minutes.