For the base
Drain the apricots in a sieve, but catch the juice. Mix the butter, sugar, eggs, flour and baking powder to make a smooth batter. Turn the batter into a springform pan, buttered and sprinkled with breadcrumbs. Arrange the apricots evenly on the batter.
For the filling
Make up the vanilla pudding according to the package instructions using the apricot juice and sugar, and pour the pudding over the apricots while still hot.
(Alternatively, mix the cornstarch and vanilla flavoring with a little of the apricot juice. Bring the remaining juice to a boil. Stir the mixed cornstarch into the boiling juice and boil for one minute. Continue as above)
Bake the cake in a preheated oven (190°C) for 35-40 minutes.
For the topping
Separate the eggs. Mix the egg yolks with the sugar and sour cream.
Beat the egg whites until they form stiff peaks and fold into the egg yolk mixture.
Spread on the hot cake and return to the oven for a further 15-20 minutes.
Let cool for at least 1 hour before releasing from the springform pan.
Dust with confectioners' sugar and serve.