Bittersweet and glossy. Use this to fill and frost any chocolate butter cake. Prepare just before using. Melt in a double boiler, a heatproof bowl set over a pan of barely simmering water, or in a microwave-safe bowl:

Melt, stirring frequently. If using a microwave, melt on 50 percent power in 20-second bursts, stirring after each interval. Remove from the heat and stir in—do not beat—just until combined:

Use immediately. If the frosting becomes too stiff or loses its gloss at any time, set the bowl in a larger pan of hot water for a few seconds and stir to soften. This keeps, refrigerated, for up to 1 week.