How do I know when the plum butter is done cooking?
Early on in the cooking process the mixture will be thin and watery. After you puree the fruit butter you’ll have a smooth mixture but you’ll most likely want to thicken it a bit further. There are two good indications that help you know when the mixture is fully cooked. First, dip a spoon into the fruit butter. (It will be hot so be careful.) Run you finger down the back of the spoon and if the two sides stay put (and don’t rush in to coat the spoon right away), then your fruit butter is in good shape. The second way to observe the cooking process is to scoop up a bit of the mixture and let it drip back into the saucepan. Early in the simmering time, the fruit butter will fall back into the pan in separate drips. Later on when the mixture is cooked, it will slide off the spoon in sheets and in a more uniform way. The fruit spread will continue to thicken as it cools.