Place the springform pan rim (26 cm Ø) on a lightly oiled cake plate. Melt butter at low heat. Let it cool down a little. Mix well with muesli. Spread on the cake plate as a cake base and press down well. Chill for about 1 hour
Drain the apricots, collecting the juice
Mix the jelly powder and sugar. Mix with 200 ml apricot juice. Warm up while stirring constantly until everything is dissolved (do not boil!). Let it cool down
Puree half the apricots. Mix with sour cream and vanilla sugar. Stir in the jelly. Chill for about 15 minutes until it begins to gel. Whip cream until stiff and fold into the jelly mixture
Spread a little cream on the muesli base. Place the rest of the apricots on top and spread with the rest of the cream. Chill for at least 4 hours. Decorate with melon and lemon slices