Melt the duck fat, goose fat or butter in a non-stick pan, allow it to get nice and hot, then add the chopped streaky bacon rashers. As it begins to brown, add the finely sliced onion and the chopped garlic clove.
Next, add the sliced cooked Brussels sprouts or shredded boiled cabbage and let it colour slightly. All this will take 5-6 mins.
Add the cold mashed potato. Work everything together in the pan and push it down so that the mixture covers the base of the pan.
Allow the mixture to catch slightly on the base of the pan before turning it over and doing the same again. It’s the bits of potato that catch in the pan that define the term ‘bubble and squeak’, so be brave and let the mixture colour.