Grease a 24-inch square springform pan or a 26-inch round springform pan. Line the edge with a strip of parchment paper.
Wash, core and quarter the apricots.
Beat 4 egg whites with a pinch of salt and slowly pour in 100 g of sugar and beat until thick and frothy.
Mix the 4 egg yolks with the remaining 100 g sugar until thick and creamy.
Melt the butter a little in lukewarm milk (the butter should not be completely runny), add the vanilla sugar and the rum (or lemon zest) to the yolk mixture and stir.
Using a whisk, gently fold in the flour mixed with baking powder and the whipped egg white / sugar mixture.
Put a good 2/3 of the dough in the prepared baking pan.
Spread the apricots densely on top (if necessary add a little sugar over the apricots) - if desired, sprinkle some cinnamon on top and then cover with the remaining batter. It just needs to be a thin layer of dough. Sprinkle with flaked almonds.
Bake at about 175-180 degrees hot air on the middle rack for about 40-45 minutes.