Preheat the oven to 350°F.
To make the batter: In the bowl of a stand mixer fitted with the whisk attachment, add the egg whites. Whisk, starting on low to avoid splattering; gradually increase the speed to high until stiff peaks form. Remove the egg whites from the mixing bowl and transfer to a separate bowl. Set aside.
In the bowl of the stand mixer fitted with the whisk attachment (no need to wash the bowl), add the butter, cane sugar, and vanilla extract. Mix on low until combined and no chunks of butter remain. Add the milk and mix on low until combined, scraping down the sides of the bowl as needed.
In a separate bowl, add the cake flour, baking powder, and sea salt and whisk together. Add the cake flour mixture to the butter mixture and continue to mix on low until combined, scraping down the sides of the bowl as needed.
Remove the bowl from the stand mixer and add in the egg whites; fold with a spatula until you have a smooth batter.
Line a 9x13-inch cake pan with parchment paper, and butter and flour the sides. Pour the batter into the cake pan and spread evenly. Bake for 30 to 35 minutes, or until a toothpick inserted in the center comes out clean. Allow the cake to cool completely before removing it from the pan.
To make the whipped cream: In the bowl of a stand mixer fitted with the whisk attachment, add the heavy whipping cream, cane sugar, and vanilla extract. Mix on low and gradually increase speed until mixture starts to thicken, until you are at full speed. Whisk until stiff peaks form.
Transfer the whipped cream to the top of the cake and spread evenly. Top with sliced strawberries.
Store in an airtight container in the fridge for up to 3 days.