Use room-temperature ingredients for a tender crumb and to help the batter emulsify properly. Natural cocoa powder is traditional for red velvet and reacts with vinegar and baking soda for a lighter texture. If using frozen raspberries, do not thaw; toss them lightly in a teaspoon of flour before folding to minimize bleeding. For deeper red color, adjust food coloring gradually to avoid a bitter taste. Ensure the white chocolate ganache is fully cool before adding to frosting or it may loosen the icing; if frosting becomes soft, chill it briefly and rewhip. To prevent doming, avoid overmixing and bake cakes on the center rack. The cake layers can be baked a day ahead, wrapped well, and chilled for easier assembly, and the finished cake slices cleanest with a warm, wiped knife.