Pre-heat the oven to 175C°/gas mark 4. Put the duck legs in a tight fitting pan with the duck fat, garlic, bay leaf, thyme and peppercorns. Add a teaspoon of sea salt, cover with a lid or foil and cook in the oven for about an hour and a half or until the meat is soft and coming away from the bone. Leave the fat to cool a little and strain into a container or preserving jar and store in the fridge to use for roasting potatoes.
Take a spoonful or so of the duck fat and fry the onions in a covered, thick-bottomed pan for 5-6 minutes until they are soft, stirring occasionally. Then remove the lid and turn up the heat to give them a little colour. Put them into a mixing bowl.
Heat some more duck fat in a frying pan (cast-iron, preferably) until it is very hot and cook the potatoes a few at a time on a high heat until they are lightly coloured, then add them to the onions. Remove the meat from the duck legs and cut into chunks with the skin about the same size as the potatoes. Mix well and season; add Worcestershire sauce to taste.
Divide the mixture and mould into four flat, roughly 8cm cakes with the help of a stainless steel mould or just by hand with a palette knife, then refrigerate for a couple of hours or overnight.
Press the breadcrumbs into the cakes then heat some oil in preferably a non-stick frying pan and cook for about 3-4 minutes on each side until they are golden and crisp. Keep them warm in the oven once they are cooked.
When all the hashes are cooked, fry four duck eggs, transfer the hashes to warm plates and slide a fried egg on to each hash.