Roots, ham and caramelised onion pie

Method

1. Put the onions into a bowl, pour over a kettle of boiling water and soak for 5 minutes. Drain, halve and peel. Melt 50g of the butter in a large pan over a very low heat, then add the onions and cook, covered, for 15-20 minutes, stirring occasionally, until tender. Increase the heat to medium, add the thyme and sugar and cook, uncovered, for 5-6 minutes, until caramelised. Cool.
2. Meanwhile, put the rest of the vegetables into a steamer or colander over a pan of boiling water, cover, and steam for 10-12 minutes, until tender. Drain well and toss together with the ham and onions.
3. Preheat the oven to 200°C/fan180°C/gas 6. Make the sauce. Melt the remaining butter in a pan over a medium heat. Add the flour and cook, stirring, for 1 minute. Gradually stir in the milk and cook, stirring, until smooth and thickened. Simmer for 2 minutes, stirring continuously. Remove from the heat and stir in the cheese and parsley. Season.
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5. Pour the sauce over the vegetables and ham, and stir well. Spoon into a 2-litre pie dish. Unroll the pastry on a lightly floured surface and cut out a shape about 2cm bigger than the dish. Cover the dish with the pastry, trim the edges and use the trimmings to decorate the top of the pie.
6. Brush the pastry with the egg and make a snip in the top for the steam to escape. Sit on a baking sheet and bake for 40 minutes, until golden.