Prep your pans: Grease and line two or three 8-inch round cake pans with parchment. Preheat the oven to 350°F (175°C).
Whisk dry ingredients: In a bowl, whisk cake flour, baking powder, baking soda, and salt.
Set aside.
Cream butter and sugar: Beat butter and sugar on medium-high until pale and fluffy, about 3 minutes. Add eggs one at a time, mixing well, then add vanilla.
Add wet and dry: Mix milk and sour cream together. Add dry ingredients in three additions, alternating with the milk mixture.
Start and end with dry. Mix until just combined.
Bake the layers: Divide batter evenly among pans. Bake 22–26 minutes, or until a toothpick comes out clean and the centers spring back.
Cool in pans 10 minutes; then turn out onto racks to cool completely.
Make the Swiss meringue: Whisk egg whites and sugar in a heatproof bowl over a simmering pot (not touching water) until sugar dissolves and the mixture reaches warm-to-hot and feels smooth (about 160°F/71°C if using a thermometer). Remove from heat.
Whip to meringue: Beat the warm mixture on high until glossy, stiff peaks form and the bowl feels cool, 8–10 minutes.
Add butter: With mixer on medium, add butter a few cubes at a time. It may look curdled—keep mixing.
Add vanilla and salt. For a floral spin, mix in rose water or a spoonful of strained strawberry jam.
Color the buttercream: Set aside about one-third for white. Tint the rest pale pink with gel color.
For an ombre look, tint a small portion slightly deeper pink.
Level and fill: Level cooled cake layers if needed. Place the first layer on a board. Spread an even layer of pink buttercream.
Repeat with remaining layers.
Crumb coat: Apply a thin layer of white buttercream around the cake to lock in crumbs. Chill 20–30 minutes until set.
Final coat and smooth: Frost the cake with white buttercream on top and sides. For a pink ombre, add the pale pink around the bottom third and blend upward with a scraper.
Chill briefly.
Pipe rosettes: Fit a piping bag with a star tip and fill with darker pink. Pipe small rosettes along the top edge or cluster them on one side. Add a few white rosettes for contrast.
Add flowers safely: Wrap flower stems in floral tape or use food-safe stem covers.
Tuck them into the buttercream, avoiding direct stem-to-cake contact. Keep blooms minimal and airy.
Finishing touches: Add edible pearls or a dusting of sparkle. Chill 15 minutes to set, then bring to room temperature before serving for the best texture.