Wash 1 lime hot, grate dry and thinly grate half of the peel. Halve both limes, squeeze the juice. Cream fat, vanilla sugar, lime zest and 200 g sugar with the whisks of the hand mixer.
Stir in the eggs one by one. Mix flour and baking powder and alternate with yoghurt and about half of the lime juice. Pour the dough into a greased and floured Frankfurt wreath form (approx. 24 cm Ø; 2 litres capacity) and bake in a preheated oven (electric cooker: 175 °C/ circulating air: 150 °C/ gas: see
manufacturer) bake for 35-45 minutes (stick sample).
Remove the cake from the oven, let it cool down for about 20 minutes and turn it over. Let the cake cool down on a cake rack. In the meantime, cut the lemon in half and squeeze the juice. Put blueberries and remaining lime juice in a pot, bring to the boil and simmer covered for 3-4 minutes.
Then puree finely and pass through a sieve. Fill up blueberry puree with water to 200 ml. Put it back into the pot with 30 g sugar, bring to the boil.
Stir starch and 2-3 tablespoons of cold water until smooth, stir into the blueberry mixture, simmer for about 1 minute. Stir egg yolks and 3 tbsp. blueberry mixture until smooth, mix with the remaining blueberry mixture.
Add butter in flakes, bring to the boil while stirring until the butter has melted. Pour blueberry curd into a bowl, cover surface immediately with foil and let cool for about 30 minutes.
Cut the cake 3 times horizontally. Remove 1 tbsp. curd and pour into a bowl, cover with foil, put aside. Spread the rest of the blueberry curd on the cut surfaces of the lower 3 dough rings and spread.
Put the cake back together. Chill the cake for about 1 hour.
Squeeze the juice of the lemon. Stir cream cheese, lemon juice and icing sugar until smooth. Remove approx. 1/3 cream cheese cream, mix with blueberry curd. Spread the cake with the white cream cheese cream all around, then marble with blueberry cream.
Keep cool until serving.