Strawberry Vanilla Cake
1 cup (8 oz.) unsalted butter, softened, plus more for pans
2 cups granulated sugar
2 large eggs
2 teaspoons fresh lemon juice (from 1 lemon)
1 teaspoon vanilla extract
2 1/2 cups (about 9 3/8 oz.) bleached cake flour (such as Swans Down), plus more for pans
2 tablespoons strawberry-flavored gelatin (from 1 [3-oz.] envelope)
1/2 teaspoon baking soda
1/4 teaspoon table salt
1 cup whole buttermilk
1 cup chopped fresh strawberries
2 cups (1 lb.) unsalted butter, softened
7 cups (about 28 oz.) unsifted powdered sugar
2 teaspoons vanilla extract
1/8 teaspoon kosher salt
1/2 cup heavy whipping cream
Whole and halved fresh strawberries
Prepare the Cake Layers: Preheat oven to 350°F. Beat butter with an electric mixer on medium speed until creamy, about 1 minute. Gradually add sugar, beating until light and fluffy, 4 to 5 minutes. Add eggs 1 at a time, beating until combined after each addition. Beat in lemon juice and vanilla until combined.
Stir together flour, gelatin, baking soda, and salt in a bowl; add to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating on low speed until just combined. Fold in chopped strawberries.
Grease 3 (8-inch) round cake pans with butter, and line pan bottoms with parchment paper. Grease parchment with butter, and dust insides of pans with flour. Spoon batter evenly among prepared pans, and smooth tops.
Bake in preheated oven until a wooden pick inserted in centers of cakes comes out clean, 26 to 30 minutes. Cool in pans on wire racks 10 minutes. Invert cakes onto wire racks; let cool completely, about 1 hour.
Prepare the Vanilla Buttercream: Beat butter with a stand mixer fitted with a paddle attachment on medium speed until creamy, 1 to 2 minutes. Reduce mixer speed to low; gradually add powdered sugar, beating until smooth, about 2 minutes, stopping to scrape down sides of bowl as needed. Beat in vanilla and salt. Increase mixer speed to medium; gradually add cream, beating until fluffy and spreadable, about 30 seconds.
Place 1 Cake Layer on a serving plate or a cake stand. Top with about 3/4 cup Vanilla Buttercream, spreading over top to edge of layer. Top with second Cake Layer; repeat spreading process with 3/4 cup Vanilla Buttercream.
Top with remaining Cake Layer. Frost top and sides of whole cake with remaining Vanilla Buttercream. Decorate with whole and halved strawberries.