- 1/4 cup (1/2 stick) butter
- 5 cups chopped leeks (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 (about 4 cups packed)
- 1 tablespoon Dijon mustard
- 1 teaspoon hot pepper sauce
- 2 large eggs
- 1 pound penne pasta
- 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. Remove from heat. Season cheese sauce to taste with salt.
- 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. do ahead Can be made 2 hours ahead. Let stand at room temperature.
- Preheat oven to 400°F. 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.