1. Cake: Preheat oven to 325 degrees. Butter two 9-inch round cake pans and two 6-inch round cake pans. Line with parchment; butter parchment. In a large bowl, whisk together flour, 1 cup granulated sugar, baking powder, and salt. In another large bowl, whisk together oil, egg yolks, milk, lemon zest, and vanilla seeds. Whisk egg-yolk mixture into flour mixture.

2. In the bowl of an electric mixer fitted with the whisk attachment, beat egg whites on high speed until frothy. Add cream of tartar and beat until soft peaks form. Gradually add remaining 3/4 cup plus 2 tablespoons granulated sugar, beating until stiff, glossy peaks form, about 5 minutes. Whisk one-third of egg white mixture into batter. Gently but thoroughly fold in remaining egg-white mixture with a rubber spatula. Transfer batter to prepared pans: 2 cups batter in each 6-inch pan and 4 cups batter in each 9-inch pan. Bake until golden and tops spring back when lightly touched, about 25 minutes for 6-inch cakes and 30 minutes for 9-inch cakes. Let cool in pans on wire racks 10 minutes. Invert cakes onto racks; remove parchment. Let cool completely, upside-down.

3. Whipped Cream: In the bowl of an electric mixer fitted with the whisk attachment, beat together cream and confectioners' sugar on medium speed until stiff peaks form. Cover with plastic wrap and refrigerate.

4. Using a serrated knife, trim tops of cakes flat. Split each cake horizontally into two equal layers. Place a 9-inch cake layer, bottom-side down, on a serving platter. Spread 1 1/2 cups whipped cream evenly over top. Repeat process with remaining 9-inch cake layers, spreading 1 1/2 cups whipped cream between each layer and leaving top layer (bottom-side up) uncovered. Refrigerate while you work on the second tier. Repeat process with 6-inch cake layers, spreading 1 cup whipped cream between each layer.

5. Insert a wooden dowel or skewer into 9-inch tier; trim dowel so that it?s 1/4 inch taller than height of tier. Trim 2 more dowels to same height. Arrange dowels in a circular pattern, about 3 inches from edge of cake. Center 6-inch tier over 9-inch tier, pressing gently to secure. Insert a dowel into 6-inch tier; trim dowel to height of tier.

6. Garnish cake with berries and flowers, scattering on top of each tier and around perimeter of serving platter. Using a small, fine sieve, sift confectioners' sugar over berries. Serve immediately.