Preheat your oven to 350°F (176°C). Grease and line the cake pans with parchment paper.
Sift the flour, sugar, baking powder, and salt into the bowl of your stand mixer fitted with the paddle attachment (or large mixing bowl if using a hand mixer). Set the mixer to the lowest speed and blend until well combined.
With the mixer running on low speed, slowly add the butter to the bowl. Mix until fine crumbs have formed and no large clumps of butter remain.
In a medium mixing bowl, combine the eggs, egg whites, buttermilk, sour cream, and vanilla extract. Whisk to combine.
With the mixer on low, pour the wet ingredients into the bowl of your stand mixer (or large mixing bowl) in a slow and steady stream. Mix until barely incorporated, scraping down the sides of the bowl when necessary. Increase the mixer speed to medium and beat until creamy, no longer than 1 to 2 minutes.
Divide the cake batter evenly among the prepared pans. Bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean.
Allow the cakes to cool in their pans for 15 minutes before inverting them onto wire racks to cool completely before decorating.
Place the cream cheese into a microwave safe bowl and heat for 15 second bursts until completely softened, stirring in between. Set aside.
Add the butter to a saucepan and place onto the stove over medium heat. Once melted, add the brown sugar and stir until smooth.
Reduce the heat to low and stir in the softened cream cheese and vanilla.
Transfer the mixture to the bowl of your stand mixer (or large mixing bowl), cover, and allow it to reach room temperature.
Once cool, place the bowl onto your stand mixer (or use a hand mixer) and whip until fluffy. Fold in the powdered sugar and dried hibiscus flower powder and mix until well incorporated.
Using a large offset spatula, fill and frost the cooled cake in the hibiscus frosting. Slice and enjoy! Cake is best if eaten within 3-4 days. Store in the fridge for up to 1 week.