Place frozen blueberries in a sieve to drain excess water as they thaw. This prevents the cake from becoming soggy.

Mix room-temperature butter, egg yolks, and sugar with a spatula until well combined.

Sift half a cup of flour and add half the milk. Mix well, then add the remaining flour and milk and mix again.

Whisk egg whites until stiff peaks form.

Fold half of the whipped egg whites into the batter gently, then add the remaining half and mix until combined.

Mix drained blueberries with 1 tbsp sugar and 1 tbsp flour just before adding them to the batter.

Add the prepared blueberries to the batter and mix gently.

Line a baking pan with parchment paper, grease it, and pour in the batter.