Put the plaice fillets on a plate inside a steamer and steam for 3-4 minutes until cooked. Meanwhile, wilt the spinach in a little butter and keep warm. Heat the rest of the butter in a pan, cook the shallots until softened then turn up the heat until the butter turns a golden brown colour. Take off the heat, add the shrimp, parsley and a squeeze of lemon. Season. Sit each plaice fillet on a mound of spinach and spoon the butter over.