Peel the apples and cut into even slices. Add to a 6-quart slow cooker along with the brown sugar, sugar, cinnamon, salt, vanilla bean paste (or extract), cornstarch and 1 tablespoon butter, stirring to combine.
Cover and cook on low for 4 hours, or high for 2 hours, or until the apples are tender and cooked to your liking but not mushy. Uncover and quickly stir every 2 hours on low or every 1 hour on high to check for doneness and to avoid potential burning.
Add the remaining 1 tablespoon butter, stirring to combine. Serve warm, at room temperature or chilled.
