For the cream cheese frosting:
Preheat the oven to 170°C.
Put the butter and sugar in a mixer with a paddle attachment and beat until light and fluffy. Add the eggs, the vanilla extract, the flour, and baking powder and keep beating until well mixed. Add the soured cream and mix until creamy.Gently stir in the blueberries by hand until evenly dispersed. Pour the mixture into the prepared mould and bake in the preheated oven for 40 minutes, or until golden brown and the sponge bounces back when touched. Leave the cake to cool slightly in the mould before turning out to cool completely. When the cake is cold, put it on a serving plate, cover the top and sides with the cream cheese frosting and decorate with more blueberries.