1. Wash kumquats. Trim a tiny slice from each end and make 3 slashes, crosswise, in each fruit, leaving the seeds in. Place in a large saucepan, cover with water, and bring to a boil over high heat. Reduce heat and simmer for 10 minutes.
2. Strain the liquid into a glass measuring cup and measure. If needed, add enough water to make 3 cups; otherwise, return 3 cups of the liquid to thepan and discard any remaining liquid. Add vinegar, sugar, cinnamon, cloves, and lemon slices. Bring to a simmer over high heat. Reduce heat and simmer for 5 minutes. Remove from heat, cover, and let sit overnight at room temperature.
3. The next day, have ready 7 clean 8 oz. jelly jars and lids. Fill a large stockpot with water and bring to a boil over high heat. Simmer while you finish preparing the kumquats. Place empty jars in the water to keep them hot.
4. Bring kumquat mixture to a boil over high heat. Reduce heat and simmer until the mixture thickens into a syrup, about 1 hour.
5. Drain all water from heated jars. Pour kumquats into the prepared jars, being sure to distribute both syrup and fruit evenly; leave about 1/2 inch of space at the top of each jar. Screw on lids. Place in simmering water, making sure the water completely covers the jars by 1 to 2 inches; you may need todo this in batches. Raise heat to bring water to a boil. Boil jars for 5 minutes, then remove jars and allow to cool to room temperature, about 4 hours. Once cool, the lids should be flat.
Source: Hannaford fresh Magazine, November - December 2010