In a small saucepan, blend whipping cream and sour cream with a whisk.
Heat to 90F (30C) over low heat.
Do not allow mixture to become hotter or culture will be inhibited and cream will not thicken.
Pour into a warm sterilized glass jar or bowl; cover lightly.
Store in a dark place 8 to 12 hours or until cream ripens and becomes thick.
Refrigerate after ripening.
Cream will continue to slightly thicken.
Refrigerate 24 hours for best flavor.