1. Preheat the oven to 190°C, gas mark 5. Cook the pasta in boiling, lightly salted water for 12 minutes or until tender. Meanwhile, heat
1 tablespoon of the oil in a large saucepan and gently fry the chicken in 2 batches, each for 3 minutes. Return all the chicken to the pan, add the onion and fry for a further 5 minutes. Remove from the heat.
2. Pull the tarragon leaves from the sprigs and add to the pan with the broad beans, cheese sauce and milk. Drain the pasta, add to the pan and mix well. Turn into a shallow ovenproof dish.
3. Combine the breadcrumbs with the remaining oil and spoon on top. Bake for 30 minutes until bubbling and golden, and the chicken is cooked through with no pink meat.