Grease an oblong loaf or cake tin. Roll out thawed pastry into a large oblong about the thickness of a penny. Cut off a piece of pastry to fit top of loaf and reserve. Use remainder to line base and sides of tin.
In a mixing bowl, combine sausagemeat, onion, sage and breadcrumbs. Bind with beaten egg, reserving a little for glazing pastry. Turn mixture into pastry-lined tin and press hard-boiled eggs down in the centre, covering them with sausagemeat.
Put on pastry lid. Trim corners and seal edges. Roll out trimmings and cut decorative "leaves". Make a small hole in centre of pie to allow steam to escape. Flute edges of pastry. Brush with reserved beaten egg, put pastry leaves in position, and brush these, too. Bake in a pre-heated, hot oven (425 F, gas mark 6) for 10 to 15 minutes until pastry has set. Then reduce heat to moderate (375F gas mark 4) and continue baking for a further 30 minutes. Serve hot with cooked vegetables, or serve cold with salad or pickles.