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.

In a large mixing bowl, sift together the all-purpose flour, cornstarch, baking powder, baking soda, and salt.

In a stand mixer, combine granulated sugar and lemon zest, rub them together, then add the softened butter and beat on medium speed until light and fluffy.

Add the eggs to the butter mixture, mixing well after each addition. Gradually add half of the sifted dry ingredients on low speed.

Mix in sour cream, vegetable oil, lemon juice, lemon extract, and vanilla extract, then gradually add the remaining dry ingredients.

Divide the batter equally among the cake pans. Bake each layer for 20-23 minutes or until a toothpick comes out clean.

For the raspberry buttercream, sift powdered sugar and raspberry powder. Whip the butter until fluffy, then incorporate the sugar mixture and whole milk.

Once the cake layers have cooled, place one on a serving plate, spread raspberry buttercream, and raspberry jam, then repeat with the second layer.

Apply a crumb coat around the cake before the final frosting layer and decorate with fresh raspberries and lemon slices.