First, make the pastry. Put the plain flour, fava bean flour, salt and butter in the bowl of a food processor and mix at the lowest setting until it looks like fine breadcrumbs. Add the egg and the water. The mixture should form into a pliable ball. If necessary add a very small amount more water, but only a little at a time. Remove from the food processor bowl, flatten the ball slightly to a thick disc shape (this makes it easier to roll out later), wrap in clingfilm and put it the fridge for 30 minutes.
In the meantime, bring a pan of water to the boil, add the broad beans and return to the boil for two minutes. Immediately remove from the heat, drain the broad beans and plunge into a bowl of ice cold water. Slip the emerald broad beans out of their skins and set to one side.
Pre heat the oven to 175?C (350?F, gas mark 4). Grease a flan dish. Retrieve the pastry, roll out thinly and carefully place it into the flan dish. Trim the pastry so that there is a slight overhang of about 1 cm. (Any unused pastry can be frozen for use in the future). Prick the base and sides of the flan pastry base with a fork and line it with parchment and baking stones or beans. Bake blind in the preheated oven for 10 minutes. Remove from the oven, leave to cool slightly and then remove the parchment and baking beans. The edges of the flan will have shrunk slightly, but now you can trim them neatly to the height of the flan dish with a sharp knife.
Whisk the eggs with the double cream and sea salt until smooth.
Pour half of the egg and cream mix into the pastry shell. On top of this evenly sprinkle half of the Cheddar cheese. Next, evenly distribute three quarters of the chopped herbs.
Pour most of the remaining egg and cream mixture on top, followed by most of the remaining Cheddar cheese. Next, carefully arrange the asparagus across the tart. Scatter the broad beans around the asparagus, followed by the remaining herbs. Finally, top with the remaining egg and cream mixture and any remaining cheese.
Place in the pre-heated oven for 35-40 minutes until set and golden. Leave to cool slightly. Serve while still warm with a simple green salad.
