Preheat your oven to 325 degrees. Spray a 9×13 metal pan on the bottom, line with parchment paper, and spray again. If you need to use metal binder clips to hold down the sides, remember to use metal, not plastic. Set aside

In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, cream the butter, and sugar on medium speed until fluffy and smooth, about 3 minutes.

With a rubber spatula, scrape the bottom and sides of the bowl. Add the eggs, one at a time, on medium speed, beating for 20 seconds after each addition. Stir in the vanilla extract on low.

In a medium size bowl, mix together the sour cream, buttermilk, vanilla extract and vegetable oil.

Bake for about 40-43 minutes, or until a toothpick inserted into the center comes out clean.

Remove from the oven and allow the cake to cool completely in the pan on a wire rack. Once cooled, use the handle of a wooden spoon to poke about 20 holes across the cake, about three-quarters of the way through the depth of the cake.

If using fresh strawberries, hull and slice them. If using frozen strawberries, allow them to thaw slightly so they can be sliced easily.

In a medium saucepan, combine the strawberries, granulated sugar, ¼ cup of water, and lemon juice. Cook over medium heat, stirring occasionally, until the strawberries release their juices and soften, about 5-7 minutes.

Once the strawberries are softened, remove the saucepan from the heat. Use an immersion blender to puree the mixture until smooth. If you don't have an immersion blender, you can transfer the mixture to a regular blender, blend until smooth, and then return it to the saucepan.

In a small bowl, whisk together the cornstarch and the other ¼ cup of water until smooth.

Return the strawberry puree to the stove over medium heat. Stir in the cornstarch mixture and the remaining ¾ cup of water.

Cook the mixture, stirring constantly, until it begins to thicken and comes to a gentle boil. This should take about 3-5 minutes.

Once the sauce has thickened, remove it from the heat. Add the whole can of sweeten condensed milk and mix until combined. Allow it to cool slightly before using. The sauce will continue to thicken as it cools.

In a medium bowl, beat the heavy cream until stiff peaks form. Set aside.

In a separate large bowl, beat the cream cheese and butter together until smooth and creamy.

Add the powdered sugar, vanilla extract, and salt, and beat until smooth.

With a rubber spatula, gently fold in the whipped cream until well combined.

Spread the frosting evenly over the cooled sheet cake. Let the cake sit for 20 minutes before serving!