Preheat your oven to 350°F (175°C) and grease three 8-inch round cake pans to ensure the cake layers come out easily.

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until well combined.

In a large bowl, cream the softened butter and granulated sugar until fluffy. Beat in the eggs, one at a time, followed by the vanilla extract and lemon zest until well incorporated.

Gradually add the dry ingredients to the mixture, alternating with the buttermilk mixed with fresh lemon juice, until just combined.

Divide the batter evenly among the prepared pans and bake for 25-30 minutes or until a toothpick inserted into the center comes out clean. Allow the cakes to cool on wire racks.

Simmer raspberries with sugar and lemon juice in a saucepan for 5-7 minutes.

Mix cornstarch with cold water, then add this slurry to the pan to thicken. Remove from heat and let it cool.

Beat softened butter until light and fluffy. Gradually add the sifted powdered sugar, mixing in lemon juice, zest, vanilla, and salt until creamy.

Adjust the consistency with cream if necessary.

Level the cooled cake layers using a serrated knife.

Assemble the cake by spreading buttercream on each layer and filling with the raspberry filling.

Apply a crumb coat of frosting and chill the cake for a bit to set.

Frost the entire cake with the remaining buttercream and decorate with fresh raspberries and additional lemon zest.

Chill before serving for optimal flavor.