Bring a large pot of salted water to a boil. Add the beans and cook until tender, 2 to 3 minutes. Drain in a colander and transfer to an ice bath. Drain well.
Fry the bacon in a large skillet and cook, stirring, over medium-high heat until crisp and golden, 5 minutes. Add the shallots and garlic, and cook, stirring, for 2 minutes. Add the flour and cook, stirring constantly, for 2 minutes. Add the stock, salt, pepper, and vinegar, and cook, stirring, until thickened, 4 to 5 minutes. Add the green beans and cook until warmed through, about 2 minutes.
Remove from the heat and serve.
Yield: 4 servings