Preheat oven to 350°F. Grease and line three 9-inch round cake pans with parchment paper.

In a stand mixer with paddle attachment, cream butter, oil, and 1 cup sugar until light and creamy. Add vanilla and lemon zest and mix until combined.

In a medium bowl, whisk together cake flour, baking powder, and salt.

Alternately add flour mixture and milk to the creamed ingredients in thirds and halves, mixing gently after each addition. Transfer batter to a large bowl.

Clean mixer bowl thoroughly. Whip egg whites with whisk attachment until soft peaks form, slowly adding remaining sugar until stiff and glossy peaks form.

Fold a third of the egg whites into the batter to lighten it, then gently fold in remaining whites until well combined.

Divide batter evenly into prepared pans and bake 20-25 minutes until cakes spring back and begin to pull from edges. Cool in pans for 30 minutes before transferring to a wire rack to cool completely.

For lemon curd: Heat lemon juice, butter, and heavy cream in a saucepan to just under boiling. Whisk eggs, egg yolks, and sugar in a heatproof bowl.

Gradually whisk hot lemon mixture into eggs, then return all to saucepan. Cook over medium heat stirring constantly until thickened, about 5-8 minutes.

Strain curd through a sieve, whisk in salt and vanilla, cover, and refrigerate until cold.

For buttercream: Boil sugar and water without stirring until syrup reaches 238°F.

Beat eggs and egg yolks until pale. Slowly add hot syrup with mixer running, then whip until cooled to room temperature.

Add butter chunks gradually, mixing until smooth and combined. Add salt and whip again.

For lemon syrup: Boil lemon juice, water, and sugar until dissolved. Cool to room temperature.

Mix 3 cups buttercream with 1/2 cup lemon curd; set aside remaining buttercream and 1/3 cup lemon curd for decoration.

If cakes are domed, trim to level. Place cake layer on cake board. Brush with lemon syrup.

Spread 1 cup curd-buttercream mixture evenly. Pipe a border with 1/2 cup for flood layer. Spread half of the lemon curd and half the raspberries on top.

Add second layer, brush with syrup, repeat filling and flood layer with remaining curd-buttercream, curd, and raspberries.

Top with third layer, brush with syrup, then chill for 1 hour to firm.

Apply thin crumb coat with 1 cup plain buttercream and chill 30 minutes.

Frost top and sides with remaining buttercream. Spread reserved lemon curd on top and decorate with reserved raspberries and any leftover buttercream.