To make the pastry, sift the flour into a bowl and stir in the butter and water.
Press the mixture into the base and up the sides of a 20 cm (8-inch) fluted flan
tin. Prick the base with a fork and bake blind in a preheated oven 200 degrees C,
400 degrees F, Gas Mark 6 for 15 minutes, removing the lining paper and baking beans
for the last 5 minutes.
For the filling, heat the butter in a pan and add the onion, fry for 5-6 minutes
until golden. Cool slightly and spread over the base of the pastry case.
Arrange the ham and asparagus spears on top.
Beat together the eggs, cream and seasoning to taste and pour into the flan case.
Return to the oven for a further 30-35 minutes until the filling is set and golden.