Preheat the oven to 180 ° and slide the tray or grid into the second rail from below. Grease the muffin cups with a little butter. Peel the apples, cut into small cubes and drizzle with lemon juice.
Mix the butter with sugar, vanilla sugar and eggs until frothy. Mix flour, salt, baking soda and baking powder, add to the other ingredients and mix, then add milk, rum and cinnamon and mix everything together. Add a little more than half of the apples to the batter and mix in.
Pour the batter into the molds and stick the remaining apple pieces on top of the batter. Bake the muffins for 25-30 minutes.
After cooling, dust the muffins with powdered sugar.