First make your crumble topping: Mix 150g of plain flour, 150g of granulated sugar and 150g of unsalted butter. Add ground cinnamon. This will be your crumble topping which you will use again at the end of this recipe.
Now onto the cake: First of all, add yeast into a cup of warm water & leave to stand in a warm place for 10 minutes.
Mix flour, milk, granulated sugar, olive oil, vanilla sugar and one egg.
Add yeast into the mixture and make a smooth but sticky dough. Add more flour if the dough is too sticky. Leave in a warm place for about 45-60 minutes to rise.
Pour the dough in a baking dish or a tray leaving the edges slightly risen. Brush the edges with yolk from the other egg. Add blueberries and top with the crumbly topping.
Bake in a preheated over (170°C) for 20-30 minutes until the edges & topping are slightly brown.