Step 1

Preheat the oven to 200°C. In a large pan, heat oil over medium heat and cook onion for 1-2 minutes. Add celery, carrot and garlic and cook for 1 minute. Add pesto, passata, bay, thyme and stock.

Step 2

Simmer gently for 15 minutes until vegetables are cooked. Stir in lentils and season, then transfer to a 1.2-litre baking dish. Meanwhile, cook potatoes in boiling salted water until tender.

Step 3

Drain and mash. Stir in butter, milk, yolks and cheese. Spread over lentil mixture and roughen top with a fork. Bake for 15 minutes or until bubbling and golden.