In a mixer bowl, place flour, eggs, vinegar, sugar, and butter. Pour in the yeast starter and knead the dough.

Cover the bowl with the dough with a kitchen towel and set aside in a warm place to rise - for about an hour.

After this time, briefly knead the dough again.

Line a baking pan measuring approximately 20/30 cm with baking paper.

Transfer the dough to the pan and spread evenly (you can use damp hands or a spoon dipped in water).

Mix the blueberries with sugar and potato flour - sprinkle over the dough and spread in an even layer.

To prepare the crumble, rub the butter with flour and sugar until a lumpy mixture forms - sprinkle the crumble over the cake.

Cover the baking sheet with the cake with a cloth and set aside in a warm place for about 30 minutes - during this time the dough will rise a bit.

Preheat the oven to 170 degrees Celsius (top/bottom heat mode).

Bake the cake for about 40-45 minutes, until golden brown and a skewer inserted into the center comes out dry.