Homemade sour cream can be kept in the refrigerator a whole month, and it will get thicker and thicker and better and better. It can be whipped, if you make it with heavy cream, but be careful not to overwhip, as it will turn to butter in a flash.

Method: Combine cream and buttermilk in a screwtop jar. Shake the jar for a minute. Let stand at room temperature for 24 hours. If room is especially cool (on a cold winter day) let stand an extra 12 to 24 hours. Cream will thicken. Refrigerate at least 24 hours, preferably longer, before using.