Melt 1 tablespoon of the butter in a medium, heavy saucepan over medium-high heat. Add the ginger and cook, stirring, for 1 minute. Add the apples, bourbon, brown sugar, cinnamon, and salt. Simmer, uncovered, over medium-low heat until the apples are very tender, about 45 minutes.
Purée the mixture in a blender or food processor. Return the purée to the saucepan and place over medium heat. Whisk in the remaining butter, 1 tablespoon at a time. Serve immediately, or cover and keep warm until ready to serve.
Yield: about 2 cups