Peel the onions and cut them into thin slices. Put half the butter in a frying pan with the onions and fry until lightly browned. Add the mince and mix till the juice from the mince has been absorbed. Allow to stand for a short while, then pour in the wine and cook slowly for 15 to 20 minutes. Remove from heat and allow to cool.
Cut the hard-boiled eggs into pieces, and add the breadcrumbs and the beaten eggs to the mince. Butter a baking tin and spread the more significant part of the pastry in it, making sure enough is left over to cover the top; the pastry should be well greased.
Put in the mince mixture, spread it evenly over the pastry, and then cover with the rest of the pie leftover. Trim the edges and butter the outside of the pastry before baking in a moderate oven for 50 to 60 minutes.