In a small saucepan, bring your bone broth to a rolling boil over medium-high heat. Flavor it with fish sauce and/or salt to taste. Remember: it’s only as savory as you make it. Crack the egg in a small bowl and season with a few additional drops of fish sauce and a pinch of salt. Whisk well with a fork. Remove the bone broth from the heat and stir the soup with a heat-proof spatula as you slowly pour in the whisked egg. The egg should cook on contact with the hot liquid even though you’ve removed the saucepan from the heat. The eggs should be soft and wispy rather than overcooked and chunky. Transfer the soup to a bowl. The soup tastes delicious as-is, but you can fancy it up with your favorite add-ins like cilantro, scallions, and/or chili peppers.