Preheat the oven to 325 degrees F. Spray 2 (8-inch) round cake pans with cooking spray. Dust lightly with flour and shake out the excess.
Reserve half of the raspberries, and combine the other half with 1 tablespoon sugar and crush with a fork. Set aside.
Sift together the flour, baking powder, baking soda, and salt in a medium bowl, stir with a fork to evenly combine the ingredients. In another bowl, whisk the buttermilk, oil, lemon zest, and lemon juice.
Whisk together eggs, egg whites and sugar in a large bowl and beat with an electric mixer on medium speed until it holds ribbons, about 2 minutes. Add the flour mixture in 3 parts, alternating with the buttermilk mixture in 2 parts, beginning and ending with the flour. Stir together by hand until evenly combined and no lumps remain.
Pour the batter evenly into the pans. Bake in the center of the oven until a cake tester comes out clean, about 30 minutes. Cool on a baking rack for 10 minutes, then turn the cakes out onto a baking rack to cool completely.
Frosting: Bring a few inches of water to a boil in a saucepan that can hold an electric mixer bowl above the water. Whisk the sugar, egg whites, water, cream of tartar, and salt in the bowl by hand. Set the bowl above the boiling water and beat with an electric hand mixer at medium-high speed until stiff peaks form, about 7 minutes. Remove from the heat; beat in the lemon zest and vanilla.
To assemble the cake: Place 1 layer on a flat serving or cake plate, top side down, and spread with crushed raspberries. Top with 3/4 cup frosting, spreading gently on top of the raspberries. Place the second cake layer on top, top side up, and frost the top and sides. Decorate with the reserved raspberries.
This recipe has been updated and may differ from what was originally published or broadcast.
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