Sponge Cake:
Preheat your oven to 350°F (180°C) and line the bottom of a 9-inch cake or springform pan with parchment paper.
In a bowl, whisk together the flour, baking powder, and kosher salt. Set aside.
In the bowl of a stand mixer fitted with the whisk attachment, whisk the egg whites and lemon juice (or vinegar) on medium speed until foamy.
Gradually add half of the sugar (½ cup), whisking on medium-high speed until stiff, glossy peaks form.
In the same stand mixer bowl, whisk the egg yolks and remaining sugar (½ cup) on medium speed until pale and fluffy. Slowly drizzle in the vegetable oil, followed by the warm water and vanilla extract, mixing until combined.
Sift ⅓ of the flour mixture into the egg yolk mixture and gently fold with a spatula. Fold in ⅓ of the egg whites until no streaks remain. Repeat the process with the remaining flour and egg whites.
Pour the batter into the prepared pan and bake for 25-30 minutes, or until golden brown and a toothpick inserted in the center comes out clean. Allow the cake to cool in the pan for 5 minutes, then remove it from the pan and cool completely on a wire rack.
Strawberry Simple Syrup:
While the cake cools, combine water, sugar, and sliced strawberries in a saucepan over medium heat. Stir until the sugar dissolves and the mixture is hot. Remove from heat and let cool.
Strawberry Puree (optional):
In a saucepan, cook strawberries and sugar over medium-low heat until soft and juicy, about 5-7 minutes.
Mix cornstarch with water, then add to the strawberries. Increase heat to medium-high and cook until the mixture bubbles.
Blend the mixture with an immersion blender until smooth. Let cool.
Whipped Cream Frosting:
Chill the bowl of your stand mixer and the whisk attachment in the freezer for 15 minutes.
Beat the cream cheese, powdered sugar, and vanilla on low speed until smooth.
Slowly drizzle in the cold heavy cream while mixing on medium-low speed. Once fully incorporated, increase speed to high and whip until stiff peaks form. Keep chilled until ready to use.
Cake Assembly:
Use a serrated knife to cut the cooled sponge cake into three even horizontal layers. Place the first layer onto a cake stand, sliding parchment paper under the cake to keep the stand clean.
Using a pastry brush or spoon, coat the top of the first layer with strawberry simple syrup.
Spread a layer of whipped cream frosting evenly over the cake. Add a layer of sliced strawberries, followed by another layer of whipped cream.
Place the second cake layer on top and gently press down to eliminate gaps. Repeat the process with simple syrup, whipped cream, strawberries, and whipped cream.
Brush the underside of the final cake layer with simple syrup, then place it crumb-side down on top of the cake. Press gently.
Spread the remaining whipped cream frosting evenly over the top and sides of the cake.
If using strawberry puree, swipe it onto the cake with a spatula and smooth it out to the desired texture. Serve and enjoy!