I always measure the rice with a measuring cup, so the amount is given in ml. If you use short grain rice, 100 ml is almost exactly 100 g. However, I find it very practical to measure rice and milk in a cup.
Put the rice in a saucepan (1 liter is sufficient), add the milk. Peel and core the apple, cut into small pieces and add to the rice and rice milk. Bring to the boil, stir a little.
Turn the heat back a little, to a little less than half (for me level 4 of 9). Let the rice pudding, uncovered, simmer gently for about 20-25 minutes.
Tip: You can sprinkle the rice with cinnamon. 1 level teaspoon of unsweetened cocoa powder or carob powder in rice pudding makes it chocolate milk rice.