Sip on this broth like tea, or use as a base for a more substantial soup by adding vegetables, chicken and grains or pasta.
Place chicken thighs, onion, celery, ginger and vinegar in slow cooker. Add enough water to just cover the ingredients. Cook for 8-12 hours on a setting so broth is just barely simmering. Strain broth. Reserve 4 cups of rich chicken broth; cool and refrigerate or freeze rest of broth for future use.
Trim lemongrass stalks off and bottom of lemongrass bulb. Use a mallet to crush lemongrass. Place 4 cups of chicken broth, lemongrass and ginger in a saucepan and bring to boil. Reduce heat to medium low and simmer for 10 minutes. Remove lemongrass and ginger. Season to taste with salt.