
Preheat the oven at 170ºC/340ºF and prepare a 3 x 20 cm/8-inch baking pan with parchment paper.
Sift together the flour, cornstarch, baking powder, baking soda, and salt; set aside.
In a large mixing bowl, combine sugar and lemon zest. Add butter and mix at high speed for 3 minutes, then add eggs two at a time and mix at low speed. Gradually add dry ingredients and mix, then add remaining wet ingredients and fold the batter gently.
Divide batter between prepared pans and bake for 20-23 minutes or until a cake tester comes out clean. Let cool.
Sift powdered sugar and strawberry powder. Mix butter for 4 minutes, then combine with powdered sugar and strawberry powder in two parts, whipping until fully incorporated.
Place the first cake layer on a serving dish, spread buttercream, add the second layer, repeat, and cover with a crumb coat. Chill for 20 minutes.
Add remaining buttercream, smooth out, and decorate with fresh strawberries and lemon slices.