Place the diced apples in a lightly greased slow cooker. In a medium bowl, mix the sugar, cinnamon, nutmeg, cloves, salt and vanilla.
Pour the mixture over the apples in the slow cooker and mix well. Cover and cook on high for 1 hour. Reduce heat to low and cook 8-10 hours, stirring occasionally, until the mixture is thickened and dark brown.
Uncover and continue cooking on low 1 hour. Puree with an immersion blender, if desired, to increase smoothness.
Spoon the mixture into sterile containers. Cover and refrigerate for up to 2 weeks, or freeze for up to 6 months.