Preheat the oven at 170ºC/340ºF conventional oven and prepare a 3 x20 cm/8-inch baking pan with parchment paper.
Sift together the all-purpose flour, cornstarch, baking powder, baking soda and salt and set it aside.
In a large mixing bowl add the granulated sugar and lemon zest. Rub it together to release all of the lemon zest flavor, until it looks like wet sand. Then add the butter and mix it together on high speed for 3 minutes.
Add the eggs two at a time into the mixture and mix it in until combined on low speed.
Continue by adding half the dry ingredients, on low speed, mixing until just combined.
Then add the sour cream, vegetable oil, lemon juice, vanilla extract and mix until just combined. Then add the other half of the dry ingredients and mix until combined.
Using a rubber spatula, give the batter a gentle fold to make sure all of the ingredients have combined.
Divide the cake batter into the prepared pans and bake for 20-23 minutes or until a cake tester comes out clean. They will stay light and won’t brown.
Let the cakes cool on a cooling rack. After 10 minutes, gently remove the cake from the cake tin and let the cakes cool down completely.
Sift the powdered sugar and freeze dried strawberry powder and set it aside.
Mix the butter in a stand mixer with the paddle attachment or with a hand mixer for 4 minutes on medium/high speed. Scrape down the sides of the bowl and mix for an additional 2 minutes.
Add the powdered sugar/freeze dried strawberry powder, vanilla extra and milk in 2 parts. Whipping until each addition is fully incorporated. You can optionally add a tiny bit of red food color if you want the color to be brighter.
Scrape down the sides of the bowl and give the buttercream a final mix for 2 minutes at low speed.
Place the first cake layer on your serving dish on your turntable. If you don’t have a turntable, don’t worry, you can easily decorate the cake without it.
Add 2 big scoops of buttercream and with an offset spatula, even it out. Then add the other cake layer and repeat the process. Add the last cake layer and cover the whole cake in a thin crumb coat.
Place it in the fridge for 20 minutes to set. Then add the remaining buttercream, and even it out over the cake. Optional, make a wavy design with the frosting, using the offset spatula.
Decorate with fresh strawberries and lemon slices.