27 Sweet-sour Onion Sauce

Name: Sweet-sour Onion Sauce (Sauce aigre-douce à l’oignon)
Yield: For five people
Cuisine: French
Ingredients: 1 teaspoon Dijon mustard; 1 tablespoon tomato ketchup; 2 eggs; 1 tablespoon sunflower oil; 1 tablespoon olive oil; 1 tablespoon fromage blanc; 2 tablespoons onion purée