How to Make It
Bring a large pot of water to a boil over high. Add green beans; return to a boil, and cook 2 minutes. Drain green beans, and rinse under cold running water to cool. Spread in a single layer on paper towels to drain. Let stand at room temperature until completely dry, about 45 minutes.
Meanwhile, heat olive oil in a large skillet. Add onion, and cook, stirring often, until softened, about 8 minutes. Add garlic and wine, and cook until most of the wine evaporates, about 2 minutes. Sprinkle flour over onion mixture, and cook, stirring constantly, 1 minute. Add milk, and bring to a simmer, stirring constantly. Cook, stirring constantly, until thickened, about 2 minutes. Stir in cream cheese, salt, pepper, and nutmeg until smooth.
Transfer green beans to a lightly greased 13- x 9-inch baking dish. Pour milk mixture evenly over green beans, and stir to coat. Spread in an even layer; cover with aluminum foil. Chill until ready to bake, up to 1 day ahead.
Preheat oven to 350°F. Remove casserole from refrigerator while oven preheats. Bake, covered, until hot and bubbly around the edges, about 1 hour.
While beans bake, cut leeks in half lengthwise; cut each half into 2- to 3-inch pieces. Thinly slice into long strips (about 2 cups thin strips). Heat canola oil in a small saucepan over medium-high to 350°F. Fry leeks in hot oil, in 2 to 3 batches, until golden, 1 to 2 minutes per batch. Remove with a slotted spoon, and drain on paper towels. Sprinkle fried leeks over hot casserole just before serving.