Using a palette knife, frost 1 of the 9-inch cakes with the chocolate frosting. Frost the sides first, building extra frosting at the top of the sides. Then, frost the top. Since this part of the cake is supposed to look like the center of a sunflower, the frosting should not be smooth, but should swirl into peaks. To create this swirled, peaked effect, lightly run the palette knife through the frosting and gently pull up. Using a spatula place the cake in the center of a platter that is at least 20-inches by 20-inches or you can use a piece of cardboard that is covered with foil.
To create the petals: Using a serrated knife, cut the second 9-inch cake in half. Then, cut each of the halves in half again. You should have 4 triangles. Cut each of these 4 triangles in half again to create 8 triangular pieces. Using a paring knife, trim each of the eight petals to curve slightly inward so they hug the outside of the center of the cake. Be careful not to trim off too much. Start at the corner of the curved edge, and trim a slightly rounded arc that ends at the opposite corner of the rounded edge. Using the yellow frosting and a small spatula or palette knife, frost the top and 2 sides. There is no need to frost the curved edge. Once the pieces are frosted, place them around the cake. Looking at the cake as though it was a clock, place the petals at 12, 3, 6 and 9. Place the remaining four petals in between 12 and 3, in between 3 and 6, in between 6 and 9 and in between 9 and 12.