Method

• 1

  Preheat the oven to 200C/400F/Gas 6. Place the stock in a large pan and bring to the boil, add the carrots, parsnips and new potatoes, cover, return to the boil and simmer for 15 minutes or until they are tender. Stir in the leeks and peas, return the stock to the boil then remove from the heat.

• 2

  Drain the stock and reserve. Place the vegetables in an ovenproof dish. Discard 300ml of the stock and return the rest to the pan. Mix the cornflour to a smooth paste with a little cold water and stir into the stock with the crème fraîche and tarragon.

• 3

  Bring the mixture to the boil, stirring until you have a smooth, creamy sauce. Simmer for one minute. Pour over the vegetables and season well.

• 4

  Place all the topping ingredients in a food processor with a good pinch of salt and ground black pepper; whizz together until they resemble fine breadcrumbs. (If you haven’t got a food processor, rub the butter into the flour, then stir in the mustard and cheese and rub together again until you have a crumbly mixture).

• 5

  Scatter the crumble mixture over the top of the veggies then bake for 20 minutes or until the top is golden brown.