Preheat oven to 350°F (180°C). Grease and flour a round pan (springform recommended).

Make the streusel: mix flour, salt, and 40 g sugar. Add cold butter and rub until crumbly. Refrigerate.

Separate eggs. Beat egg whites to stiff peaks; set aside.

Whisk egg yolks with remaining sugar (60 g). Add milk and vanilla, then mix in baking powder.

Fold whipped egg whites into the batter gently in 2–3 additions.

Pour batter into pan. Scatter blueberries evenly. Top with streusel crumbs.

Bake 45–55 minutes until a toothpick comes out clean. Cool 15–20 minutes before slicing.