Place half the milk, the egg, wholemeal flour and seasoning to taste in a bowl and whisk until smooth. Heat 1/2 teaspoon oil in a small frying pan and pour in sufficient batter to coat the base of the pan when tipped gently. Cook until golden then turn over and cook the other side. Repeat with remaining batter to make approximately 8 pancakes. Heat half the butter in a saucepan and add the onion and mushrooms. Fry gently for 2-3 minutes then add the spinach and cheese with seasoning to taste. Cook for a further 1 minute. Divide the filling between the pancakes, reserving excess liquid, roll up and arrange in a greased ovenproof dish. Heat the remaining butter and stir in the plain flour. Gradually add the remaining milk with any reserved liquid and cook over a medium heat for 2 minutes until smooth and thickened. Add seasoning to taste and pour over the pancakes. Cover with foil and place in a preheated oven 190 ?C, 375 F, Gas Mark 5 for 20 minutes. Sprinkle with freshly chopped parsley before serving.