1/4 cup (1/2 stick) butter
5 cups Melissa’s leeks, chopped (white and pale green parts only; about 5 large)
1/4 cup all purpose flour
3 1/2 cups whole milk
1 pound extra-sharp cheddar cheese, coarsely grated
1 tablespoon Dijon mustard
1 teaspoon hot pepper sauce
1/2 teaspoon kosher salt, more or less to taste
Freshly ground black pepper, to taste
2 large eggs
Few gratings fresh nutmeg
1 pound campanelli pasta
Preheat oven to 400°F. Lightly butter 15x10x2-inch baking dish.
Melt 1/4 cup butter in heavy large saucepan over medium heat. Add leeks; stir to coat. Cover saucepan and cook until leeks are tender, stirring occasionally, about 12 minutes (do not brown). Uncover saucepan; add flour. Stir 2 minutes. Add milk; bring to simmer, stirring often. Add cheese, mustard, and pepper sauce. Stir until cheese melts. Stir in salt and pepper. Remove from heat. Season cheese sauce to taste with salt. Stir in nutmeg.
Whisk eggs in medium bowl. Gradually whisk in 1 cup cheese sauce. Stir egg mixture into cheese sauce in saucepan.
Meanwhile, cook pasta in large pot of boiling salted water until just tender but still firm to bite, stirring occasionally. Drain. Return to pot.
Stir cheese sauce into pasta in pot. Transfer to prepared baking dish.
Bake pasta until cheese sauce is bubbling around edges and some ends of pasta are golden brown, 25 to 30 minutes. Let stand 15 minutes. Serve hot.