Chocolate Sour-Cream Icing

Set up a double boiler by placing a heatproof bowl over a saucepan of gently simmering water, ensuring the bottom of the bowl does not touch the water. Add finely chopped dark chocolate to the bowl and stir occasionally until fully melted and smooth.

Remove the bowl from the heat and allow the melted chocolate to cool slightly so it is warm but not hot to the touch. This prevents the sour cream from curdling when added.

Measure the sour cream and bring it to room temperature if it has been refrigerated. Room-temperature sour cream blends more evenly into the chocolate.

Add the sour cream to the cooled melted chocolate and stir gently with a spatula or whisk until the mixture is completely combined and glossy. Avoid over-mixing, which can cause the icing to become grainy.

Add the vanilla extract to the chocolate and sour cream mixture and stir until fully incorporated. Taste and adjust the vanilla level as desired.

If the icing appears too thin, allow it to rest at room temperature, stirring occasionally, until it thickens to a spreadable consistency. If it is too thick, warm it very gently over the double boiler for a few seconds and stir.

Use the icing immediately to frost cooled cakes or cupcakes, spreading it evenly with an offset spatula for a smooth, glossy finish. Work quickly, as the icing will begin to set as it cools.