Preheat your oven to 170ºC (340ºF) and prepare three 20 cm (8-inch) round cake pans by lining the bottoms with parchment paper and greasing the sides.

Sift together 2 cups of all-purpose flour, 1/4 cup of cornstarch, 1 teaspoon of baking powder, 1/2 teaspoon of baking soda, and 1/2 teaspoon of salt.

Combine 1 1/2 cups of granulated sugar with the zest of 2 lemons and 1 cup of softened butter. Beat on high speed for about 3 minutes until light and fluffy.

Slowly add 4 large eggs, two at a time, mixing until smooth.

Add half of the dry mixture to the batter, followed by 1/2 cup sour cream, 1/2 cup vegetable oil, 1/4 cup lemon juice, 1 teaspoon lemon extract, and 1 teaspoon vanilla extract. Mix until just combined, then fold in remaining dry mixture.

Divide the batter evenly among the prepared pans and bake for 20-23 minutes, or until a cake tester comes out clean. Let the cakes cool in their pans for about 10 minutes.

Sift together 4 cups of powdered sugar and 1/2 cup of freeze-dried raspberry powder. Beat 1 cup of softened butter until light and fluffy, then gradually add the sugar mixture with 2-4 tablespoons of whole milk.

Once the layers are cooled, place one layer on a platter, spread raspberry jam, and then a layer of raspberry buttercream. Repeat for the second layer and add the third layer.

Apply a crumb coat of buttercream to the entire cake. Chill in the fridge for about 15 minutes.

Frost the cake with a thicker layer of raspberry buttercream. Decorate with fresh raspberries and lemon slices.