Core the pears and chop them – there’s no need to peel them. Pile them into a large slow cooker (mine is a 6 quart oval. It’s better to go wide than tall with this one.) Add 1/2 cup water, cover, and cook on high for 1 hour. Uncover, stir the pears, then cover again and cook on low until the pears are all quite soft.
Use a potato masher or an immersion blender to produce a smooth applesauce-like texture. Add lemon juice and 2 cups sugar. Taste the mixture, and adjust both sugar and lemon juice to get the balance of flavors you like best. Add the spices, stir to combine.
Set the cooker to HIGH, cover, and cook at least an hour to get the pears really hot. Now reduce the heat to LOW, prop open the lid, (I laid chopsticks across the pot, then put the lid on top, leaving space for evaporation.) and cook for 10-12 hours, until reduced to half its original volume.
You can stretch this time out if your schedule demands it. To maintain the pears without evaporating, place the lid securely in place. To let it reduce again, prop the lid open. I let my batch cook, propped open, on the counter overnight while I slept. No fuss, no muss, no scorching. The finished pear butter should be thick and not at all runny. For the smoothest pear butter possible, use your immersion blender again.
Prepare jars as usual, and heat water for a boiling-water bath. When the jars are ready, fill them, and process in a boiling water bath 20 minutes.