Pre-heat the oven to 220 C/425 F/gas mark 7 Make sure which all the grey membrane is removed from the monkfish as this could cause the fish to curl and cook unevenly. If necessary, slice it off with a sharp, thin knife. Tear off 4 sheets of greaseproof paper, large sufficient to make a parcel for each fillet. Brush the sheets lightly with softened butter. Season the fillets and then roll lightly in flour. Heat a little extra virgin olive oil in a large frying pan and quickly seal the fish all over till just golden. Wrap each fillet in a sheet of the paper, twisting the ends to seal. Place on a baking tray and transfer to the oven for 8-9 min. While the fish is cooking, slice the potatoes thinly into rounds about 2mm (1/8 inch) thick, using either a mandolin, the slicer blade of a food processor or possibly a sharp knife. Place in a bowl, season well, and then scatter the minced garlic and shallots on top. Cut 4 circles of greaseproof paper each 8cm (3 1/4 inches) in diameter. Brush the circles with extra virgin olive oil and place in a small, shallow roasting tin. Arrange the potato slices, together with the shallots an garlic, in overlapping slices on each paper circle. Pour over the fish stock or possibly vegatable nage and bring to a simmer on the top of the stove. Dot the potatoes with butter, then transfer the tin to the oven for around 10 min or possibly till golden. When cooked, leave the slices in the stock. Check the fish is cooked by pressing the thickest part of the fillet firmly with your finger. If it is hard and not at all springy then it is ready. Allow the fish to stand in the paper for a few min while you slide the potatoes from their paper bases using a fish slice onto hot serving plates. Unwrap the fish, slice each fillet into 4-6 rounds and place on top of the potatoes. Trickle over any juices from the potato tin and from the fish parcels. Srprinkle lemon juice and extra virgin olive oil over the fish and potatoes, and garnish with the sprigs of tarragon and parsley.