Place the sliced leeks in a pot of boiling water and simmer for 5 minutes, until tender.
Meanwhile, soak the cubed bread in the milk and set aside.
Drain the leeks and in a mixing bowl, combine with bread, egg, and salt and pepper. Be sure to squeeze the excess milk from the bread before adding to the leek mixture. Stir well.
Divide the leek mixture into 6 equal patties. Dip both sides in flour. Set aside.
Heat the olive oil in a heavy pan and add sliced onion. Saute on medium until fragrant and it begins to soften, being careful not to burn. Remove onion from oil and save the onion another use.
Keep the onion infused oil on the heat and add the leek patties. Fry on medium for 5 mintes per side, until a crispy golden brown. Again, adjust the heat so as not to burn the patties. When done, place patties on a paper towel to absorb any excess olive oil.Serve immediately or keep in the fridge for up to 4 days.
Serve with yogurt, masharpone cheese, or as part of an antipasto platter.