I cheat, I just cook my apples with water until they are soft, I use a few different varieties at the same time. I have a chinois which is a cone shaped sieve with a wooden press, that I place a jelly bag on the outside frame. After I press the apples to get all the good stuff I let the bag drip for awhile. With the amount I do this is done in a few batches. The liquid goes in a container in the fridge and I measure the pulp in to the pan. This way the apples are cooked but not over cooked and I can make jelly also. I use the recipe that is in the Joy of cooking, but cut the spices in half. I like a milder clove taste. I think the process is probably as long as just reducing the apple butter but I can't see wasting the gas to cook the liquid out. If the butter is to thick I can always add some juice back. I usually get about 4 to 5 jars of each out of a pot of cooked apples.