Turkey and mushroom mince

Name: Turkey and mushroom mince
Cuisine: American
Ingredients: 1 tsp sunflower oil; 3 onions, finely chopped; 3 carrots, finely diced; 500g turkey thigh mince; 250g mushrooms, sliced; 1 stick celery, finely diced; 1 heaped tbsp plain flour; 1 low-salt chicken stock cube dissolved in 500ml boiling water; good pinch white pepper; 2 tsp reduced-salt soy sauce