Step 1

Cook pasta shells in boiling water until al dente. Drain and allow to cool.

Step 2

Combine butter and flour in a saucepan over a medium heat. Stir briskly until combined, add milk and whisk until mixture thickens. Add pesto, chicken and spinach. Stir until combined and spinach has wilted. Allow to cool slightly.

Step 3

Pour tomato passata into the bottom of a large greased baking dish. Stuff pasta shells with creamy mixture. Place gently on tomato sauce in rows. Sprinkle over grated cheese.

Step 4

Bake uncovered in a moderate oven until cheese has melted and browned, approx 20 mins.

Step 5

Sprinkle with fresh basil leaves just before serving.