Preheat oven to 350ºF (175ºC). For a convection oven, reduce cooking temperature by 25ºF (15ºC). Spray oil (or butter) a round 9-inch (23 cm) springform pan, lined with a round of parchment paper, and spray oil (or butter) the paper as well.
In a large bowl, cream together the butter and ¾ cup sugar.
Add egg yolks, vanilla, salt, and mix until creamy.
Sift the 1 ½ cups flour and the baking powder together into the butter mixture and gently combine.
Add the milk to the butter mixture and gently combine.
In a stand mixer (or another large bowl), beat the egg whites with ¼ cup of the sugar until quite thick and opaque.
Fold the egg whites into the batter.
Coat the berries with 1 Tbps. of the flour and add to the batter.
Pour batter into the prepared pan and drop the pan a few times to force the air bubbles out. Sprinkle the top with white sparkling sugar.
Bake at 350ºF (175ºC) for 50-60 minutes, test by inserting a skewer into the cake. When it comes out clean it's ready.
To Store
You can keep the leftovers in an airtight container and store in the refrigerator for up to 3 days or in the freezer for a month.
Notes
The recipe is adapted from Food Gal, originally adapted from “Hero Food” by Seamus Mullen.