12 ounces wide egg noodles
1⁄4 cup unsalted butter
2 large leeks, sliced
1/4 cup all-purpose flour
3 cups whole milk, at room temperature
4 cups (16 ounces) shredded Gruyčre cheese
2 tablespoons Dijon mustard
1 tablespoon lemon zest
1/2 teaspoon salt
4 (5- to 5.5-ounce) cans oil-packed tuna, drained and flaked
3 tablespoons extra-virgin olive oil
1 teaspoon minced garlic
1 cup panko (Japanese breadcrumbs)
1. Cook egg noodles until al dente according to package directions. Drain, rinse with cold water, and drain again.
2. Melt butter in a medium saucepan over medium heat. Add leeks and cook, covered, 7 minutes or until tender but not browned. Whisk in flour; cook 1 minute. Pour in milk; bring mixture to a boil over medium-high heat, whisking frequently. Reduce heat to medium-low, and simmer 3 minutes or until sauce is smooth and thickened.
3. Remove from heat, and whisk in cheese and next 3 ingredients. Fold in tuna and egg noodles. Pour into a greased 3-quart baking dish.
4. Combine olive oil, garlic, and panko; sprinkle over casserole. Bake at 375° for 30 minutes or until golden brown and bubbly. Let stand 5 minutes before serving.