Parmesan Mousse

Bring cream to just below a boil in a large saucepan over high. Reduce heat to low. Simmer, stirring often, until reduced by 1/2 cup, about 20 minutes. During last 3 minutes of cooking, whisk in cheese and salt until completely melted and smooth. Transfer mixture to a heatproof bowl, and refrigerate until thickened and cool, about 1 hour. Transfer to a piping bag when ready to use.