Cut the veg into rough chunks, then put them in a bowl and mix with the cheese. Season well with freshly ground black pepper. Shape into 8 patties and dust with flour.
Heat half the oil and butter and cook 4 patties for 3-4 minutes on each side, until golden. Repeat with the remaining oil and butter and the patties.
Bring a pan of water to the boil, then turn down to a simmer. Pour in the vinegar and then carefully break each egg in to the water. Cook for 1½ minutes, then remove with a slotted spoon.
Serve 2 patties for each person with a poached egg and some watercress leaves.
Cook's tip: you can use all sorts of cooked leftover veg to make these delicious bubble and squeak patties - sprouts, broccoli, peas or whatever else is in your fridge.