For the chicken liver salad, remove the sinew from the livers and, if the livers are quite large, cut them in half. Set aside.
Arrange the mixed salad leaves over the base of one large serving plate.
For the croutons, remove the crusts from the bread and cut the rest into 1cm/½ inch cubes.
Heat the clarified butter over a medium heat in a frying pan. Add the bread cubes and stir well to coat in the butter. Fry for 4-5 minutes, stirring frequently, until the bread is golden-brown and crisp. Drain on kitchen paper and set aside.
Heat the clarified butter for the livers in a large, heavy-based frying pan over a high heat. Season the chicken livers with salt and freshly ground black pepper, then fry for 1-2 minutes on both sides, or until the livers are golden-brown all over but still slightly pink in the middle. Remove from the heat and allow to cool slightly before arranging on top of the salad leaves.
For the perry vinegar dressing, return the pan used to cook the livers to the heat and add the perry vinegar, mustard and sugar. Stir well with a wooden spoon, scraping up any browned bits from the bottom of the pan. Transfer to a small bowl.
Add the sunflower and walnut oil to the perry vinegar mixture and season with salt and freshly ground black pepper. Whisk together until well combined, then drizzle the dressing over the chicken liver salad.
To serve, scatter over the chives and the croutons and serve while the livers are still hot.