How to Make It
Bring a medium saucepan of lightly salted water to a boil. Add the green beans and boil until tender, about 5 minutes. Drain the beans and pat dry.
Meanwhile, in a medium bowl, whisk together the shallot, vinegar and mustard. Whisk in the extra-virgin olive oil and season with salt and pepper. Add the beans and toss well.
Season the calf's liver with salt and pepper and dust all over with the flour, tapping off any excess. In a very large skillet, heat the pure olive oil until shimmering. Add the calf's liver slices and cook over moderately high heat, turning the slices once, until they're golden, 3 to 4 minutes.
Add the frisée to the beans and toss to coat. Serve the liver with the beans and salad.