In a chilled mixing bowl, whip heavy cream with a balloon whisk or electric mixer until stiff. If using quince jelly, gently melt it over a double boiler until smooth. Gently mix sweetener of your choice into the whipped cream. Serve immediately.
Save leftover cream by spooning it into a sieve lined with a double layer of cheesecloth. Set the sieve about 2 inches over a bowl, cover tightly, and place in the refrigerator for up to 48 hours.
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