Heat a teaspoon of olive oil in a skillet over medium heat. Add the onions and shallots then cook for 6 minutes, stirring often, or until softened. Add the garlic and sauté, stirring constantly, for 1 minute. Add the beef broth; cook for 4 minutes or until the onions are really tender and the liquid almost evaporates. Add the green beans and vinegar; cover and cook for 4 minutes or until the beans are crisp-tender. Remove from heat and stir in 1 tsp of butter then season with sea salt and freshly cracked pepper, to taste. Enjoy.