Preheat the oven to 350℉. Position rack to middle.
In a small bowl, combine the brown sugar, flour, oats, cinnamon and nutmeg. Set aside.
Wash the apples.
Cut apples in half (see note). Remove seeds and core with melon baller or spoon.
Pour hot water, vanilla (if using) and rhum (if using) in bottom of the pan.
Place apple halves in a baking dish and sprinkle tops with the mixture.
Top each apple with 1/6 tablespoon of butter.
Bake uncovered for 25-30 minutes or until you can pierce the apples easily with a fork. Baste occasionally with infused water.
Alternately, you can core the apples and spoon the mixture in the hollowed out cavity. Increase bake time to 45 minutes. Remember to score apples 1/4 inch from the top. Make one complete incision around the apple. (This allows the apple to expand while baking.1 serving= one apple halfPlease keep in mind that the nutritional information provided below is just a rough estimate and variations can occur depending on the specific ingredients used.