Heat the cream in a small saucepan until just below boiling — around 190°F to 200°F/88°C to 93°C (Do not allow the cream to come to a boil. If it does, allow it to cool to the correct temperature before moving on to the next step).
Place chocolate and salt in a medium bowl and pour over the hot cream. Let stand for 5 minutes. Whisk until the chocolate has melted completely and the mixture is smooth.
Allow to cool to room temperature, cover with plastic wrap, and set aside to cool and thicken. It will fully cool within 3 hours at room temperature (see notes for more information). Refrigerating will expedite things, but the frosting may not set evenly. Stir often as it sets in the refrigerator so it remains even and smooth.
For Whipped Frosting
Once the chocolate ganache cools completely, whip it on medium-high speed until light in color and fluffy in texture, about 4 minutes.
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Notes
At room temperature (68–72°F), expect your ganache to reach a spreadable consistency in about 1½ to 2 hours. For a firm, pipeable texture, you’ll need to wait 2½ to 3 hours.
Use good quality chocolate that's around 54-55% Cocoa solids
This recipe makes about 2 cups of frosting, which is enough for 12-16 cupcakes, a 9×13 inch cake, an 8″ layer cake, or a 9″ layer cake (a thin layer of frosting including filling).
The salt is to cut sweetness, but totally optional.
Boiling can cause a skin to form on cream so I recommend not boiling. Heating until just before boiling point will do.
Let the mixture cool completely to room temperature before covering it with plastic wrap. Covering it too early can cause condensation, which may drip into the frosting.
You can skip the whipping if you don't have a mixer. Just stir every fifteen minutes with a whisk as it chills. The frosting will be denser and yield a slightly smaller amount.
If you use the fridge to set your ganache and it gets too hard, just leave it at room temperature until soft enough to whip.