Preheat oven to 180°C (350°F) static heat.
grease and flour the pan, then remove the excess.
Peel the apples, remove the core, and cut them into slices about 1 cm (0.4 inches) thick. Arrange them in the pan.
Melt butter.
Sift the flour into a large bowl and mix with the sugar, vanilla sugar, vanilla powder and a pinch of salt.
Make a well in the center of the flour and crack the eggs into it, then mix from the center outwards to avoid lumps. Whisk well.
Add the warm melted butter and stir to incorporate.
Stir in half the milk, then add the rest. Mix well.
Note: Normally, you will have a smooth, lump-free batter. However, you can strain it through a fine sieve before pouring it over the apples.
Pour the batter over the apples and bake for 50 minutes, more or less, depending on your oven (check for doneness 15 minutes before the end of the indicated time). The clafoutis should not move and should be golden-brown. Check the doneness by inserting a skewer into the clafoutis; it should come out clean. Remove it from the oven and place it on a wire rack. Serve warm or at room temperature. If you want to enjoy it cold, let it cool completely before placing it in the refrigerator.
Dust it with a little powdered sugar before serving, but this is optional.