1. Preheat oven to 350 degrees. Line bottoms of two 9-inch round cake pans with parchment paper; brush with butter, and dust with flour. Tap out excess, and set aside.

2. In a medium bowl, combine cake flour with baking powder. In another medium bowl, whisk together egg yolks and 1/2 cup granulated sugar until mixture is thick and pale. Using a large rubber spatula, gently fold flour mixture into yolk mixture in two batches.

3. Place egg whites in the bowl of an electric mixer fitted with the whisk attachment. Beat on low speed just until they are frothy. With machine running on high speed, gradually add remaining 1/2 cup granulated sugar and the salt; continue beating until mixture is combined and stiff peaks form, about 4 minutes. Gently fold egg-white mixture into egg-yolk mixture in three batches until batter is smooth and uniform in color.

4. Divide batter among prepared pans. Bake until cake is nicely golden and springs back when touched in the center, about 20 minutes. Transfer to a wire rack; let cool 20 minutes in pan. Carefully invert cakes onto wire rack, and let cool completely before frosting.

5. Make frosting: Combine cream, confectioners' sugar, and vanilla in the bowl of an electric mixer fitted with the whisk attachment. Beat on medium speed until mixture is smooth and thick.

6. Using a serrated knife, split each cake horizontally into two layers. Set aside smoothest top layer. Spread one of the bottom layers with 1/2 cup jam and 3/4 cup frosting. Repeat with remaining bottom layer and top layer, stacking each on top of the other as they are filled. Place reserved layer on top of stacked layers; spread top with remaining 1 1/2 cups jam, and sides with remaining frosting. Garnish cake with fresh flowers, if desired. Slice into serving pieces; garnish each serving with fresh berries.