Peel the onion and cut into half rings. Sauté the onion until lightly caramelized, 3 minutes. Wash the pear and cut into thin slices. Simmer the pear in the pan for 1 minute. Wash the liver, dry with paper towels and divide into parts. Chop the walnuts and lightly dry them in a dry frying pan.
Lightly salt and pepper the liver and quickly fry on both sides in vegetable oil for 5 minutes. Cool the finished liver. Place onion, pear and liver in a deep salad bowl. Sprinkle prepared walnuts on top.
For the dressing, mix white wine vinegar with salt. Then add mustard and honey and whisk the resulting mass with a whisk until smooth. Gradually pour in the olive oil, whisking constantly until emulsified. Season with ground black pepper and dried basil.
Before serving, season the salad with mustard sauce and garnish with pear slices.