Looking for a fun way to use up Thanksgiving leftovers? Try these crispy/creamy turkey and mashed potato croquettes. Served with cranberry sauce and turkey gravy for dipping, they are a great second round for you and your holiday guests to enjoy.
Melt the butter in a large skillet over medium-high heat. Add the leek and cook until tender and translucent, 2 to 4 minutes. Stir in the chopped sage and 3 tablespoons of the flour, then continue to cook until the flour is completely absorbed into the butter mixture and lightly toasted, 1 to 2 minutes. While continually stirring, gradually pour in the milk and continue to cook until a thick bechamel forms, about 1 minute more. Remove from the heat, then stir in the turkey, mashed potatoes, a pinch of salt and several grinds of black pepper. Taste and adjust the seasoning with more salt and pepper. Transfer to a bowl and refrigerate until completely cool, about 30 minutes.
Meanwhile, set up a 3-stage breading station by placing the remaining 1/2 cup flour in a shallow bowl or baking dish, the eggs in a separate shallow bowl or baking dish and finally the panko in a third shallow bowl or baking dish. Season each with a pinch of salt and pepper. Using a 3/4-ounce cookie scoop, divide the chilled filling into about 18 pieces. Roll into uniform balls and/or 2 1/2-inch-long batons. Coat each piece in the flour, shaking the excess off, then dip in the egg to coat. Finally, dip and press into the panko, turning until evenly coated.
Fill a large, heavy-bottomed pot with enough oil to go 2 inches up the sides and insert a deep-frying thermometer. Set the oil over medium-high heat and bring to 350 degrees F. Working in 2 batches, deep-fry the croquettes until deep golden brown and heated through, about 2 minutes. Drain on a paper towel-lined plate and season with a pinch of salt. Fry the whole sage leaves until crisp, about 1 minute. Drain on the paper towel line plate as well. Serve with cranberry sauce and turkey gravy for dipping.