Prepare a boiling water bath canner and enough jars to hold three pints.
In a large pot, combine the pears, cranberries, sugar, lemon zest and juice, cinnamon, ginger, nutmeg, and cloves. Stir well, until the sugar has started to dissolve.
Set the pot on the stove over high heat and bring to a boil.
Once the mixture has started bubble vigorously, reduce the heat to medium-high and cook, stirring regularly, until the pears soften and the cranberries have all popped. If the jam seems a little too tight and the cranberries haven't all popped, add a splash of water to loosen it up.
When the pears are tender, the cranberries have popped, and the jam seems nicely thick, it is done (budget 20-25 minutes of active cooking time).
Remove the pot from the heat and funnel the finished jam into the prepared jars. Wipe the rims, apply the lids and rings, and process in a boiling water bath canner for 10 minutes.
When the time is up, remove the jars from the canner and set them on a folded kitchen towel to cool.
Sealed jars can be stored in the pantry. Any unsealed jars should be refrigerated and used promptly.