Watercress and feta tart

115g unsalted butter
225g plain flour
1 med egg yolk
1-2 tbsp water
3 med eggs
250ml semi skimmed milk
75g watercress
100g spinach leaves
large handful each of fresh mint and coriander
100g Greek feta cheese,crumbled
15g hard cheese,grated
2 handfuls pine nuts

Preheat the oven to 180c/fan 170c/gas 4.To make the pastry,rub the butter into the flour to make fine breadcrumbs,add the egg yolk and water and bring together.Roll out the pastry and use to line a 25cm round tart tin,prick the base with a fork and chill for 10 mins.Cover with foil and baking beans and place on a hot baking tray and bake blind for 10 mins.Remove the foil and beans and bake for a futher 5 mins.Meanwhile,beat the eggs and milk in a bowl.Chop watercress,spinach,mint and coriander.Add to the bowl.Pour the mixture into the tart,scatter over both cheesees and  pine nuts.Bake for 25 mins until golden.