How to Make It
In a large bowl, mix the shallot with the vinegar. Add a generous pinch each of salt and pepper and let stand for 5 minutes, then whisk in the olive oil.
Melt the butter in a small skillet. Add the walnuts and cook over moderately high heat, stirring, until golden and fragrant, about 5 minutes. Transfer the walnuts to paper towels, sprinkle with salt and let cool.
Add the endives and frisée to the dressing and toss well. Add the walnuts and cheese, toss again and serve.