Low waste chicken lasagne

Name: Low waste chicken lasagne
Prep time: 20 min
Cook time: 1 h 30 min
Total time: 1 h 30 min
Yield: 6 portions
Ingredients: 1 brown onion; 1 carrot; 1 celery stalk; 4 garlic cloves; 20 g olive oil; 2 tsp dried oregano; 2 tsp dried basil; 400 g tomato passata; 2 tbsp tomato paste; 2 tsp sugar; 250 g water; 2 tsp Chicken stock paste; ground black pepper; 500 g cooked chicken; 250 g cheddar cheese; 50 g plain flour; 50 g unsalted butter; 500 g milk; 1 tsp Dijon mustard; sea salt; 250 g dried lasagne sheets