Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans with butter, lining the bottoms with parchment paper.

In a large mixing bowl, cream together 1 cup of salted butter and 1 ½ cups of sugar using an electric mixer until light and fluffy, about 2-3 minutes.

Whisk together 2 ½ cups of cake flour, 1 tablespoon of baking powder, and ½ teaspoon of salt in a separate bowl. Gradually add in 1 cup of milk and 1 teaspoon of almond extract to the butter mixture until just incorporated.

In a clean bowl, beat 7 large egg whites until stiff peaks form. Fold the whipped egg whites into the batter in three additions.

Pour the batter evenly into the prepared cake pans and bake for 24-27 minutes until lightly golden and springy to touch.

Cool the cakes in the pans for about 10-15 minutes, then transfer to wire racks to cool completely.

In a saucepan, combine 2 cups of blackberries and ½ cup of sugar. Simmer until the berries soften, then mix 2 tablespoons cornstarch with 2 tablespoons water and stir into the berry mixture until thickened. Allow to cool.

Blend 1 cup of blackberries with 2 tablespoons of lemon juice. Mix this purée with 1 ½ cups of powdered sugar and ½ cup of softened butter until fluffy.

Spread blackberry filling on one layer of cake, add frosting, then add the second layer upside down. Frost the top and sides with the remaining frosting.

Garnish with fresh blackberries or almond slices if desired.