Place cherries in a large, heavy-bottomed saucepan or preserving kettle. Slice lemon and cut each slice into quarters; add to cherries. Pour sugar evenly over mixture and let stand until sugar dissolves.

Bring to a boil, stirring constantly, and boil rapidly, stirring all the while, for 15 minutes. Reduce heat and simmer until jam forms a set. Pour into hot sterilized jars and seal. Makes about four (8-ounce//250 g) jars.

Tip:
To test for a set: Before starting the jam, place two small plates in the freezer to chill. When ready to test jam for jell formation, remove jam from heat, drop a teaspoonful on a cold plate and return to freezer for 2 minutes.

Run your finger through the cooled jam. If the surface wrinkles, the setting point has been reached. If not, cook a couple of minutes longer, then test again on the second chilled plate. Repeat, if necessary.