4 medium leeks, trimmed, washed free-of sand, white and pale green parts coarsely chopped (about 3 cups)
1 medium-large (baking) potato, scrubbed but left unpeeled
1 slice seedless rye, semolina, light sourdough, challah, or other flavorful bread, crust discarded, bread torn into pieces
2 tablespoons chopped fresh dill
Salt and freshly ground black pepper
2 large eggs, beaten
Olive or vegetable oil, for frying
Put the leeks and potato in a medium saucepan with enough cold, salted water to cover by 1 inch. Bring the water to a boil and simmer for about 40 minutes, or until potato is tender. Drain the vegetables well. When the potato is cool enough to handle, peel it and force it through a ricer or a food mill fitted with the medium disk into a large bowl or mash. Squeeze the leeks with your hands to extract all excess moisture. Place the leeks and the bread in a food processor, puree, and add it to the potato. Stir in the dill, salt and pepper to taste, and just enough of the beaten eggs (about 2 tablespoons) to form the mixture into 2 inch croquettes. Reserve the remaining eggs, covered and refrigerated. Cover the croquettes with plastic wrap and refrigerate for about 25 minutes.
Place the reserved beaten eggs in a shallow bowl near the stove. In a 10 to 12 inch heavy skillet, heat ¼ inch oil until hot but not smoking. Dip each croquette into the egg, letting the excess drip back into the bowl, then slip it gently into the hot oil. Fry the croquettes in batches, turning carefully once, until golden brown on both sides. Drain on paper towels.