You can easily substitute cranberry jam if lingonberry jam is unavailable. Or you can substitute raw IQF lingonberries or cranberries, in which case you will need to cook them first, adding some sugar. This tea cake provides a nice change of pace, as the lingonberries add a special slightly tart flavor and also keep the cake moist. I have a passion for these small northern berries which grow wild in many sunny openings in the Scandinavian forest and other northern regions. I would probably love any recipe that featured them.