For the filling, heat the olive oil in a large frying pan over a medium heat and fry the onion and garlic for five minutes or until softened. Add the mince and cook for five minutes, stirring occasionally, or until browned and cooked through.
Stir in the rest of the filling ingredients, season with salt and freshly ground black pepper and set aside to cool.
Preheat the oven to 180C/350F/Gas 4.
For the suet pastry, sift the flour into a mixing bowl with the suet and season with salt and freshly ground black pepper. Gradually mix in about four tablespoons of cold water, or until you have a moist but firm dough.
On a lightly floured work surface roll the dough out to a 2mm thickness.
Generously butter two individual pie dishes then line each with the suet pastry, so that it covers the base and sides completely. Divide the filling mixture between the two dishes.
For the pie crust, roll out the shortcrust pastry on a lightly floured work surface to a 2mm thickness and use it to cover the two pies, pushing down the edges to seal. Brush generously with the egg yolk and make a hole in the middle of the lid to allow steam to escape.
Place the pie dishes into a deep-sided roasting tin and pour in enough boiling water to come halfway up the sides of the pie dishes, taking care not to get any water on the pastry. Transfer to the oven and cook for 20-30 minutes, or until the pastry is crisp and golden and the filling steaming hot.
Meanwhile, for the mashed potatoes, steam (or boil) the potatoes for 20 minutes or until tender. Scald the milk then mash the potatoes with the hot milk, butter and plenty of salt and freshly ground black pepper until smooth. Drizzle with a little chilli oil, if using, and keep warm.
For the parsley liquor, melt the butter in a saucepan over a medium heat and whisk in the cornflour to make a paste. Gradually stir in the stock, bring to a simmer, then stir in the parsley and garlic and stir until thickened and smooth.
Serve the hot pies with the mash, parsley liquor and jellied eels on the side.