For the Filling:
Wash blueberries in a colander under running water.
Place blueberries, sugar, lemon juice, and zest in a saucepan.
Bring the mixture to a boil slowly, stirring continuously. Let the berries cook for 3 minutes, ensuring they remain whole.
Dissolve pudding powder or cornstarch with 5 tbsp cold water and add to the blueberries. Stir until the color becomes red and let bubble up once.
Set aside to cool before pouring the filling into the baking pan.
For the Shortcrust Pastry:
Sift flour and baking powder into a bowl. Add sugar, vanilla, and salt.
Create a well in the center, add the egg, and scatter cubed butter on top.
Knead the mixture until smooth. The dough should no longer be sticky.
Line a springform pan with parchment paper. Use more than half the dough to cover the bottom of the pan, pressing it up the sides.
Form two dough rolls and press them along the sides of the pan (about 2 inches high). Seal the edges and prick the dough with a fork.
Pour the blueberry filling over the pastry.
For the Crumbles:
Combine flour, sugar, vanilla, and butter in a bowl.
Knead the mixture with your hands until crumbles form.
Evenly distribute the crumbles over the blueberry filling.
Baking:
Preheat oven to 182°C (360°F).
Bake the cake on the middle rack for 40-45 minutes. Move the cake one rack higher for the last 5 minutes for a golden crumble.
Cool in the pan before transferring to a serving plate. Dust with powdered sugar and serve with whipped cream.