In a large, oven safe pot, combine the apples, apple cider, brown sugar and salt over medium heat. Bring the mixture to a simmer, cover, and let cook for 30 minutes, stirring every few minutes.
Remove from the heat and stir in the lemon juice, cinnamon, nutmeg, and vanilla.
Using an immersion blender, puree the apples until no chunks are left (unless you want small chunks of apple in your butter). You can also carefully transfer the mixture to a blender and puree it that way.
Place the uncovered pot in the oven and bake for 3-4 hours, stirring about every half hour. The baking time is really up to you, your apples, and your oven. I found that the longer I bake it, the thicker and darker the butter becomes. Mine was baked for just over 3 hours.
Once done, remove from oven, let cool, and store in an airtight container in the fridge for up to 2 weeks.
Notes
**I used Ida Red apples with a few Cortland thrown in as well. You can use a variety of different apples and you can use several different kinds of apples in one apple butter recipe. Other varieties that work well: braeburn, Cortland, Fuji, grimes golden, jonamac, liberty, and McIntoshLightly adapted from http://www.foodnetwork.com/recipes/food-network-kitchens/homemade-apple-butter.html?oc=linkback