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1
Sift the flours, salt; mustard powder and cayenne into a bowl, and then rub in the margarine until you get a crumbly mixture.
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2
Stir in the cheese and add enough cold water to make dough that leaves the bowl clean.
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3
Wrap the dough in plastic and put in the fridge for 30 minutes.
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4
Melt the butter in a heavy based frying pan, add the onions, get them coated in the butter, cook them uncovered on a medium heat for approx 30 minutes, they have to be reduced and turned a deep brown.
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5
Stir from time to time, if they are still pale at the end of the cooking time, turn up the heat and cook for another 10 minutes until they have the right color.
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6
Preheat oven to 350F and put a baking sheet in the oven.
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7
Grease an 8 inch fluted flan tin, roll out the pastry and line the tin, prick the base with a fork, place the tin on the baking sheet in the oven and bake for 15 minutes.
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8
Remove from the oven and brush with some beaten egg (from the filling) return to the oven for 5 minutes.
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9
Then spread the onions all over the base of the flan, mix the eggs with the milk, salt and pepper, and pour as much as possible over the onions, you might have some left it depends on how much the onions have reduced.
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10
Sprinkle the cheese over the top and bake for 30 minutes (on the baking sheet again) or until the filling is golden brown and puffy.
