Heat the butter in a frying pan and cook the onions for 2-3 minutes, until slightly soft and translucent.
Place the mashed potatoes, cooked onions, turkey, cabbage and salt and pepper into a bowl and mix well.
Add the olive oil and a few dry breadcrumbs to form a firm but not stiff mixture.
Form the mixture into 4 balls, flatten on both sides to make thick cakes, and dust with flour. Brush the cakes all over with egg and coat with more breadcrumbs.
Heat a couple of tablespoons of vegetable oil in a frying pan and cook the cakes on both sides for 3 minutes until golden brown.
Place a little watercress on a warm plate, top with a cake, and a poached egg on top. Serve with French beans and hollandaise sauce.
© Phil Vickery