For the rice casserole, cook long grain rice, milk, 1 pinch of salt and lemon zest and a handful of raisins until a porridge is formed. Separate eggs. Cream butter, sugar and egg yolks. Stir butter mixture into rice porridge.
Beat egg whites to egg whites and mix gently. Peel the apple. Grease a gratin dish with a little butter. Pour in half of the rice mixture, top with coarsely torn apple and a few raisins.
Then pour in the rest of the rice mixture. Bake in the oven at 160 °C for 40 to 50 minutes.
Portion the rice casserole onto plates and serve with plum toast.