This will need to be made at least 6 hours or a 1-2 days in advance.
In a medium size sauce pan on medium heat, add the strawberries and water and slowly stir until the strawberries are somewhat covered in the water.
Add in the sugar, lemon juice, and the pinch of salt. Let it start to simmer and bring to a small boil. Stirring occasionally so the bottom doesn’t burn. You do not want a roaring boil. Just a subtle boil.
Once there is a small boil, reduce the heat to medium-low and let the mixture slowly simmer. The berries will start to break up and the mixture will start reducing in size. This takes approximately 20-25 minutes. With a rubber spatula, occasionally stir so the mixture doesn’t burn.
The mixture is done when the strawberries have formed into a jelly like substance. If your mixture is slightly watery or liquidity, let the mixture keep cooking a little longer until it has become thicker.
The end result will have about 2 cups of reduction. Once the mixture is done, remove from the pan and transfer to a heat proof container. Let it completely cool before letting it sit in the fridge for a few hours.
(Note: when you are using it in the cake batter, make sure the mixture is ROOM TEMPERATURE, not hot or cold. That will result in uneven cake layers.
Your strawberry reduction can be stored in an air tight container for up to two weeks, or in the freezer for 3-6 months.
For the strawberry cake layers
Preheat the oven to 325 degrees. Prepare three 8-inch or four 6-inch round cake pans by lightly spraying the bottom of the pan with cooking spray. Line with parchment paper and spray again. Set aside.
In a medium sized bowl, whisk together the flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter, oil, and sugar on medium-high speed until light and fluffy, about 4 minutes. With a rubber spatula, scrape the bottom and sides of the bowl.
With the mixer on medium speed, start adding the egg whites, one at a time, beating after each addition. I usually beat each egg white for about 30 seconds. Scrape the sides and bottom of the bowl after each addition. Once all the egg whites are added, on medium low speed, beat for 30 more seconds.
Add the vanilla extract, strawberry reduction, and the strawberry emulsion. Slowly mix on medium low speed for a minute.
With the mixer on low and add ⅓ of the flour and ½ of the buttermilk to the butter mixture and mix ON LOW until almost incorporated. Add another ⅓ of the flour and the rest of the buttermilk. Mix just until a few streaks of flour remain, then add the rest of the flour mixture. Mix just until the flour streaks are mostly gone.
With a rubber spatula, fold in the sprinkles.
Evenly distribute the cake batter among the three 8-inch or four 6-inch pans and bake for 30-33 minutes or until a toothpick comes out with just a few moist crumbs on it.
Remove cakes from the oven and let them cool in the pans for 15 minutes before transferring them out of the pan and placing them on cooling racks.
When cakes are completely cooled, wrap each cake layer individually with plastic wrap and stick it in the refrigerator or freezer until you’re ready to frost.
For the cream cheese buttercream
In the bowl of an electric mixer, combine the butter and cream cheese. Beat on medium speed for about two minutes. Scrape down the sides and bottom of the bowl. Beat again for 2 more minutes.
With the mixer on low speed, add the powdered sugar, followed by the cream, vanilla, and a pinch of salt. Beat on low just until mixed. With a rubber spatula, scrape down the sides of the bowl.
Turn the mixer up to medium-high speed and beat for about 3 to 5 minutes.
With a rubber spatula fold in the rainbow sprinkles.
Assembly
Place the first cake layer, top side up. Add about 1 cup of frosting. Spread over the cake layer as evenly as possible to the edges of the cake.
Repeat this step until you get to the final cake layer, which you will lay top side down.
Apply a thin coat of buttercream around the entire cake to lock in the crumbs. Freeze for about 10 minutes.
After the crumb coat is set, I went for a naked looking cake. I applied another thin layer of frosting around the cake. I wanted the pink edges of the cake to come through. I used a wilton 8B to obtain the pipped shells and then garnished with a few extra sprinkles.
This cake is served best at room temperature. Wrap the cake in plastic wrap and it can be stored in the fridge for up to 5 days. You can also wrap each individual slice in plastic wrap and store in the freezer for up to 30 days.