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1
Set the oven to 400F
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2
Cook the pasta in boiling water for 10-14 mins, or as directed on the packet, until just tender, then drain well.
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3
Meanwhile, heat the oil in a pan.
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4
Add the onion and cook it over a medium heat for 4-5 mins, until it starts to soften.
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5
Add ground beef and celery to pan and cook for a further 5-8 mins, stirring well so the meat browns all over.
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6
Add flour to the pan and cook for a further minute, stirring until the mixture has thickened, then stir in the tomatoes and 2/3 cup boiling water.
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7
Stir well while the mixture comes to the boil.
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8
Stir in stock cube, then add the Worcestershire sauce and seasoning to taste.
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9
Simmer for 2-3 minutes Remove the pan from heat and stir in drained pasta.
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10
Tip the mixture out into a gratin dish and level the surface.
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11
To make the topping, melt the butter in a pan and add flour.
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12
Cook for 1-2 mins until mixture forms a thick paste, then gradually pour in the milk, beating well and allowing mixture to come to the boil between each addition of liquid.
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13
Remove pan from heat and add mustard powder and half the cheese.
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14
Season to taste.
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15
Spoon sauce over pasta, spreading it to cover.
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16
Sprinkle remaining cheese over.
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17
Bake in the centre of the oven for 30-40 mins, or until the mixture is golden on top and sizzling hot.
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18
Serve immediately.
