3 cups flour
3 teaspoons baking powder
1 teaspoon baking soda
1 teaspoon salt
½ cup unsalted butter room temp
½ cup canola or vegetable oil
2 cups sugar
4 large eggs
1 tablespoon vanilla extract
1 ⅓ cups whole buttermilk
½ cup lemon juice mixed with 2 tablespoons powder sugar
1 pound powdered sugar
1 cup unsalted butter, softened
1 teaspoon vanilla extract
8 ounces mascarpone cheese, softened
1. Preheat oven to 350°F. Coat a half-sheet pan with cooking spray, and line bottom of pan with parchment paper or use a silpat.
2. Sift cake flour, baking powder, and salt together in a medium bowl. Set aside.
3. Beat butter and oil in a large bowl with an electric mixer on medium-high speed until smooth and creamy. Add sugar, and beat until light and fluffy. Add eggs, 1 at a time, and beat until well blended. Beat in vanilla.
4. Add flour mixture, 1 cup at a time, to butter mixture alternately with buttermilk, beginning and ending with flour mixture. Beat on low just until smooth after each addition. (Do not over beat or cake will be tough.) Spread batter evenly in prepared sheet pan.
5. Bake in center of preheated oven for 18 to 22 minutes.
6. Heat lemon juice and sugar mix in a small saucepan over low heat just until warmed through. Brush cake lightly with about half of the syrup. Cool cake completely in pan, about 45 minutes. Freeze cooled cake, uncovered, until very cold and very firm, about
7. Meanwhile, prepare the Buttercream. Beat butter and sugar in a large bowl with an electric mixer on medium-high speed until thick and creamy. Beat in vanilla. Add mascarpone cheese, and beat on low speed just until combined. Scrape down sides of bowl as needed. (Do not over mix or the mascarpone will start to break down and the frosting will become too thin.)
8. Fit a large disposable piping bag with a large star tip. Fill piping bag with 3 cups of the Buttercream. Remove cake from freezer. Using a 2 3/4-inch round cutter, carefully cut 16 circles from sheet cake.
9. Brush top and sides of each cake circle with reserved remaining lemon syrup. Pipe a tight spiral of icing on 8 of the cake layers. Top each frosted layer with unfrosted cake layer to make 8 miniature 2-layer cakes. Repeat with remaining cakes.
10. Pipe a rosette of Buttercream on top of each cake. Garnish with fresh berries, or edible flowers.