Heat butter in saucepan, add onion and cook for three minutes. Stir in flour and mustard. Blend in milk and fish stock and stir until thickened. Add flaked fish, mushrooms, parsley, mace and chopped eggs to the sauce and blend. Place in 9 inch pie dish and cover with crust.
FOR THE CRUST: Place margarine, water and half the flour in mixing bowl and cream with fork until well mixed. Stir in remaining flour to make a firm dough. Place on a lightly floured board and knead until smooth. Roll into a circle, fold and cut several gashes in top. Unfold carefully over pie filling. Bake at 425°F for 35 to 40 minutes.
The Irish Heritage Cookbook Mercedes McLoughlin and Marian McSpiritt.