How to Make It
In a small saucepan, bring the cream to a simmer over low heat. Stir in the butter until melted, then whisk in the Parmesan until smooth. Add the Fontina and cook, whisking, until the cheese is melted and the sauce is smooth, about 3 minutes. Remove from the heat, stir in the grappa and season the sauce lightly with salt. Serve at once.