Preheat your oven to 170ºC (340ºF) and prepare three 20 cm (8-inch) round cake pans.

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

Combine granulated sugar and lemon zest, then add room temperature butter and beat until fluffy.

Incorporate eggs one by one, ensuring each is fully mixed before adding the next.

Gradually add half of the dry ingredients, then mix in sour cream, vegetable oil, lemon juice, lemon extract, and vanilla extract.

Fold in remaining dry ingredients until no flour streaks remain. Ensure not to overmix.

Divide the batter into prepared pans and bake for 20-23 minutes or until a cake tester comes out clean.

Let cakes cool in pans for 10 minutes before transferring to a wire rack.

Sift powdered sugar and raspberry powder together. Beat room temperature butter until fluffy, then gradually mix in sugar and whole milk.

Spread raspberry jam and buttercream between the cooled cake layers, stacking them. Apply a crumb coat with buttercream and chill for 20 minutes.

Frost the top and sides of the cake with remaining buttercream and decorate with fresh raspberries and lemon slices.