Preheat your oven to 170ºC (340ºF). Line three 20 cm (8-inch) baking pans with parchment paper and lightly grease the sides.

In a large mixing bowl, sift together the flour, cornstarch, baking powder, baking soda, and salt. Set aside.

In a separate bowl, combine the sugar with lemon zest and rub together. Beat in the softened butter until fluffy. Add eggs, mixing well after each addition.

Gently alternate adding the dry ingredients with the sour cream, vegetable oil, lemon juice, and vanilla extract until just combined.

Divide the batter into prepared pans and bake for 20-23 minutes, or until a toothpick comes out clean. Cool in pans for 10 minutes.

Sift together the powdered sugar and strawberry powder. Beat the room-temperature butter, gradually mixing in sugar and milk until smooth.

Once the cakes are cool, place one layer on a plate, spread buttercream on top, and repeat with remaining layers. Apply a crumb coat and refrigerate for 20 minutes.

After chilling, apply a final layer of buttercream and decorate with fresh strawberries and lemon slices.