The light and moist cake layers are infused with lavender and lemon, while the tangy blackberry jam filling adds a burst of fruity sweetness.
For cake: Preheat oven to 325°F. Grease 4 6-inch cake pans with butter, and line with parchment paper rounds. Dust pans with flour.
Whisk flour, baking powder and salt together in a large bowl. Combine buttermilk, lemon juice, lemon zest and lavender extract in a small bowl.
In the bowl of a stand mixer fitted with a paddle attachment, beat butter sugar together on medium speed, scraping down the sides, as needed, until light and fluffy, about 3 to 5 minutes. With the mixer running, beat in eggs, one at a time, until combined. Add the flour mixture and buttermilk mixture in 2 additions, mixing well between each addition, until just combined.
Divide batter between prepared pans. Bake until a toothpick inserted into the center comes out clean, about 25 to 30 minutes. Let cakes cool in pans for 10 minutes. Invertonto wire racks and let cool completely.5. For buttercream and assembly: Meanwhile, whisk egg whites and sugar together in stand er bowl until combined. Bring a medium pot filled with 1-inch of water to a simmer over medium-low heat. Place bowl over simmering water, whisking frequently, until reaches 160°F, about 5 to 8 minutes. Remove from heat. Transfer bowl to stand mixer fitted with a whip attachment. Whip on medium-high speed until stiff peaks form and mixture reaches room temperature, about 17 to 20 minutes.
While the mixer is running, add butter, 1 tablespoon at a time, until a thick and fluffy buttercream forms. Add salt and lavender extract and beat until combined. Mix roughly 3 to 4 cups buttercream and lavender food coloring together, adjusting shade as desired. Set remaining white buttercream aside for later use. Transfer roughly 1 1/2 cups lavender buttercream to a piping bag fitted with a coupler attachment and tip T1.
Once cakes have cooled, create a flat cake surface by removing a 1/4-inch from the crow of the cake with cake level. Transfer one cake to a 10-inch cake drum. Place it on cake turntable. Pipe a 1/2-inch wide border around the top edge of the cake. Using an offset or straight spatula, spread roughly 1/2 cup of jam evenly over the top, right to the buttercream border. Place another cake layer on top, pressing gently to adhere. Repeat layering cakes with buttercream and jam, ending with the fourth cake layer on top.
Using an offset or straight spatula, spread a thin layer of lavender buttercream on the top and sides of cake. Refrigerate for at least 30 minutes, until buttercream is set.
Using an offset or straight spatula, spread the remaining lavender buttercream on the top and sides of cake. Smooth sides of cake by holding the spatula upright against the cake, and turning the turntable.
Divide remaining white buttercream between 6 small bowls. Add a couple of drops of each food coloring to each bowl. Stir to combine, adjusting shade as desired.
Transfer each color to a piping bag fitted with a coupler attachment. Using tip K11, pipe small green stems and leaves halfway up the side of the cake, for sunflowers, baby's breath, lavender flowers and snapdragons. Use tip K01 for blue baby's breath flowers, lavender flowers and sunflowers. Use tip K06 for snapdragon blossoms. Using tip K01, pipe a few small brown dots in the center of the sunflowers.
Slice and serve.