For the salad, lay the bacon rashers on a rack and place under the grill for 6-8 minutes, turning halfway through cooking, or until the bacon is golden-brown and crisp. Remove and drain on kitchen paper, then chop into small pieces. Set aside.
Preheat the oven to 180C/355F/Gas 4.
Place the bread cubes into a baking tray and drizzle over the olive oil. Mix well to coat, then season with salt and freshly ground black pepper. Bake in the oven for 15 minutes, or until the bread cubes are golden-brown and crisp. Remove from the oven and set aside to cool.
Heat the vegetable oil in a frying pan. Season the chicken livers with salt and freshly ground black pepper, then fry for 2-3 minutes on both sides, or until golden-brown but still slightly pink in the middle. Allow to cool slightly, then chop into bite-sized pieces.
For the dressing, whisk the mustard and raspberry vinegar together in a bowl until well combined, then gradually add the olive oil, whisking continuously. Season with salt and freshly ground black pepper and stir in the chopped tarragon.
To serve, place the frisée lettuce, red onion, chicken livers and bacon into a large bowl and gently mix together. Drizzle with the dressing, then spoon onto serving plates. Garnish each salad with a few fresh raspberries.