Preheat the oven to 350 F, position a rack in the center of the oven, and spray the bottoms of three 8-inch cake pans with non-stick baking spray.
In a large bowl, sift together the cake flour, sugar, baking powder and salt.
In another large bowl, whisk together the eggs, egg whites, buttermilk, melted butter, oil, vanilla extract and food coloring, until smooth.
Whisk everything together until combined, about 10-15 seconds. A few lumps in the batter are okay; take care not to over mix. Divide the batter between the cake pans. Tap a few times against the counter to pop any large air bubbles.
Bake the cakes for about 21-25 minutes, or until a cake tester or a toothpick comes out clean, and the tops spring back when lightly touched.
Set the pans on a wire rack, cover them loosely with a clean kitchen towel, and cool completely before frosting. When ready to frost and assemble the cake, remove the cakes from the pans.
Buttercream
In the bowl of your stand mixer fitted with the paddle attachment, beat the butter for 1 minute until smooth.
With the mixer running on low, add the powdered sugar by spoonfuls, the meringue powder and the salt, mixing until thick and combined.
Add the vanilla and food coloring; increase speed to medium and whip for 4-5 minutes, scraping the bowl down several times, until light and fluffy. Add the milk only if needed for desired consistency. Note that in warmer weather, when the butter is softer, you'll rarely need to add the milk.
Assembly and Decorating
Place one of the cooled cake layers on a cake plate. Frost with a layer of buttercream, then repeat stacking and filling all the layers. Frost the cake all over with a thin crumb coat of buttercream, then chill in the refrigerator for 30 minutes.
Fit a disposable 16-inch piping bag with tip 1M, and fill half full with buttercream. You can refill the bag as needed.
Pipe rosettes onto the sides and top of the cake, keeping them randomly placed and varying their size for the most interesting design.
Once you've covered most of the cake with rosettes, use the same piping tip to fill in any gaps with drop flowers (stars).
Notes
Leftover cake should be stored in an airtight container or cake carrier, at room temperature, for up to 3 days.If you don't have buttermilk, you can use whole milk instead, replacing 1 1/2 tbsp of the milk with lemon juice or white distilled vinegar.For a smaller cake, make half the cake recipe and use three 6-inch round cake pans. You can scale the buttercream recipe down to 2 cups of butter and 4 cups of powdered sugar.
Keyword Cake, High Altitude, Pink Velvet, Valentine's Day, Vanilla