1. Prepare Oven and Pans:

• Preheat the oven to 170°C / 340°F (conventional oven).
• Prepare three 8-inch round cake pans: grease them, line the bottoms with parchment paper circles, and grease the parchment paper.

2. Mix Dry Ingredients:

• Sift together the all-purpose flour, cornstarch, baking powder, baking soda, and salt into a medium bowl. Whisk briefly to combine and set aside.

3. Prepare Sugar and Cream Butter:

• In a large mixing bowl (preferably your stand mixer bowl), add the granulated sugar and lemon zest. Use your fingertips to rub the zest into the sugar until fragrant and the sugar looks like wet sand. This releases the lemon oils.
• Add the room temperature butter to the lemon sugar. Using the paddle attachment, beat on medium-high speed for 3 minutes until light and fluffy.

4. Add Eggs:

• Reduce mixer speed to low-medium. Add the room temperature eggs, two at a time, mixing until just combined after each addition. Scrape down the bowl.

5. Combine Batter:

• With the mixer on low speed, add half of the dry ingredient mixture. Mix until just combined (still streaky is okay).
• Add the room temperature sour cream, vegetable oil, lemon juice, and vanilla extract. Mix on low speed until just combined.
• Add the remaining half of the dry ingredients and mix on low speed only until combined and no large streaks of flour remain. Do not overmix.
• Remove the bowl from the mixer. Use a rubber spatula to give the batter a final gentle fold from the bottom up to ensure everything is incorporated.

6. Bake the Cakes:

• Divide the cake batter evenly among the three prepared pans. Smooth the tops.
• Bake for 20-23 minutes (this seems quite short for 8-inch layers, might need closer to 25-30 min – start checking early) or until a cake tester inserted into the center comes out clean. The tops should stay relatively light in color.
• Let the cakes cool in the pans on wire cooling racks for 10 minutes.  
• Carefully run a thin knife around the edges and invert the cakes onto the cooling racks. Peel off the parchment paper and let cool completely.

7. Make the Strawberry Buttercream:

• Sift the powdered sugar and freeze-dried strawberry powder together into a bowl. Set aside.
• In the clean bowl of your stand mixer fitted with the paddle attachment (or using a hand mixer), beat the room temperature butter on medium-high speed for 4 minutes until very light and fluffy.
• Scrape down the sides of the bowl and mix for an additional 2 minutes.
• Reduce speed to low. Add the sifted sugar/strawberry powder mixture in 2 parts, alternating with the vanilla extract and milk (e.g., half sugar/strawberry mix, then vanilla/milk, then remaining sugar/strawberry mix). Mix on low until each addition is incorporated.  
• Once combined, scrape down the bowl. Give the buttercream a final mix on low speed for 2 minutes to smooth it out and reduce air bubbles. (Optional: add a tiny bit of red/pink food color now if desired for brighter color).

8. Assemble the Cake:

• Ensure cake layers are completely cool. If desired, level the tops with a serrated knife.
• Place the first cake layer on your serving dish or turntable.
• Add 2 big scoops of strawberry buttercream and use an offset spatula to spread it evenly over the layer.
• Place the second cake layer on top and repeat with another layer of buttercream.
• Add the third and final cake layer, preferably upside down for a flat top.
• Apply a thin crumb coat of buttercream over the entire cake (top and sides) to seal in crumbs.
• Place the cake in the fridge for 20 minutes to set the crumb coat.

9. Final Frosting and Decoration:

• Remove the chilled cake from the fridge. Add the remaining buttercream to the top and sides.
• Use an offset spatula (and turntable if you have one) to smooth the frosting evenly.
• Optional: Create a wavy or textured design in the frosting using the offset spatula or the back of a spoon.
• Decorate the top and/or base with fresh strawberry slices/halves and thin lemon slices.
• Chill briefly before serving if desired, but serve closer to room temperature.