Add sugar and cook, stirring, until thick. Test for thickness on a chilled plate. Pour into clean hot jars and seal. The inner seal should pull down flat. If you can push it down, plink-plunk, then that seal is not tight.
Unsealed jars go in the refrigerator for immediate use.
Sealed jars will not need to be refrigerated until after they are opened. If you have any left in December, Tomato Marmalade makes a great gift. The recipes may be used and copies distributed for free as long as this notice is included. Copies may not be sold, included in publications for sale, or otherwise published in any form requiring payment to read or use without permission of the Redwood City Kiwanis Farmers Market Almanac editor.