Make a smooth batter with the flours, eggs, milk and water, then stir in the cool melted butter for extra richness and to prevent sticking during cooking. Use a 6-inch pan and make thin pancakes in the usual way, but be sure to stir the batter vigorously in between making each pancake or all the buckwheat flour will sink to the bottom of the mixture. If preparing ahead, cool the pancakes then stack them (interleaved with greaseproof paper) and wrap in a foil parcel.
To make the filling, wash and boil or steam the spinach until just tender. Chop it and squeeze out all the liquid (save the juices for a soup). Chop the onion finely and sweat it in a knob of butter until it's deliciously soft. Stir in the spinach, season with a little salt, lots of pepper and the garlic. Toast the walnuts and crumbled Stilton into the spinach mixture to give it savoury flavour and bite. Stuff the pancakes with the mixture, roll them up neatly and pile them into a lightly buttered gratin dish. Cover with foil and heat through in the oven for 25-30 minutes at 400 F (200 C) gas mark 6.
Make a smooth rich sauce with the butter, flour, stock (preferably good chicken stock) and cream. Let it simmer for about 5 minutes, stirring once or twice, then season with the cheese, mustard and salt and pepper. If the sauce is made ahead, reheat it in a double-boiler for serving, then pour it over the dish of pancakes just before bringing to table.
Source: Philippa Davenport in "Country Living" (British), February 1988. Typed for you by Karen Mintzias