Preheat oven to 350F. Grease and flour three 6" cake rounds and line with parchment.
In a medium bowl, whisk flour, baking powder, and salt until well combined. Set aside.
Using a stand mixer fitted with a paddle attachment, cream butter, orange zest, and sugar on med-high until pale and fluffy (approx 3mins). Reduce speed and add eggs one at a time fully incorporating after each addition. Add vanilla.
Alternate adding flour mixture and sangria, beginning and ending with flour (3 additions of flour and 2 of sangria). Fully incorporating after each addition.
Add fuschia color gel until desired color is reached. I added about 4 squirts.
Bake for 30-35mins or until a toothpick inserted into the center comes out mostly clean.
Place cakes on wire rack to cool for 10mins then turn out onto wire rack.
Simple Syrup:
Place sugar and water in a small pot. Stir and bring to a boil. Simmer for 1 min. Remove from heat and cool completely.
Vanilla Buttercream:
Place egg whites and sugar into the bowl of a stand mixer, whisk until combined.*
Place bowl over a double boiler on the stove and whisk constantly until the mixture is hot and no longer grainy to the touch (approx. 3mins). Or registers 160F on a candy thermometer.
Place bowl on your stand mixer and whisk on med-high until the meringue is stiff and cooled (the bowl is no longer warm to the touch (approx. 5-10mins)).
Switch to paddle attachment. Slowly add cubed butter and mix until smooth.**
Add vanilla and whip until smooth. Add fuschia color gel until desired color is reached.
Assembly:
Place one layer of cake on a cake stand or serving plate. Brush generously with simple syrup and top with approximately 2/3 cup of buttercream. Spread berries on top and gently press into the frosting.
Repeat with remaining layer and crumb coat the cake. Chill for 20mins.
Frost the top and sides of the cake and smooth with a bench scraper. Do a decorative swirl with an offset spatula if desired. Add fresh berries to the top of the cake.
Notes
* Ensure there is NO trace of egg yolks in your whites and that your mixer bowl and whisk is completely grease free or your meringue won't stiffen. ** The buttercream may look like it's curdled at some point. Keep mixing until it is completely smooth.