Heat the oven to 180°c (I use the hot air function)
Mix the butter and sugar until creamy and white
Add the eggs, one by one and mix well
Add the flour and the baking powder and mix one last time
Smear a 24 cm springform pan with butter and sprinkle it with flour
Add the mixture to the springform and equal it out
Mix sugar and cinnamon in a bowl
Peel the apples and remove the center
Cut the apples in boats and turn them in the sugar/cinnamon mixture
PLace the apples in circles starting from the outside and moving inwards until the dough is fully covered with apples
Bake the cake for 40 - 45 minutes. The cake should be medium brown and let go of the edges of the pan
Cut carefully around the edge and remove the side of the springform. Leave to cool down 15-20 minutes before to cut the cake loose from the bottom of the pan.