If there’s only one cake you ever learn to make, let it be this. Yellow cake swaddled in chocolate frosting is perhaps the defining signifier of birthdays, and for good reason–it strikes just the right balance of chocolate and vanilla. Here, we go the extra mile with a shockingly simple frosting that tastes like deluxe chocolate custard, an über-tender crumb thanks to reverse creaming and cake flour, and colorful “confetti” sprinkles inside and out. We’re celebrating, aren’t we?
When it comes to those sprinkles, choose wisely. Tiny multicolored nonpareils immediately dissolve into a streaky mess of color. Instead, look for ice-cream-parlor-style rainbow sprinkles or flat, round confetti quins (available online and at baking or craft supply stores) for distinct dashes of color.
For the silkiest frosting, bring the sour cream (and the eggs and butter while you’re at it) to room temperature. Fridge-cold sour cream will harden the melted chocolate on contact and the resulting tiny shards will be impossible to fish out. Even if you think you’re too grown-up for milk chocolate, use it anyway for a well-balanced frosting.
