1/4 cup butter
5 leeks, chopped (white and pale green parts only)
1/4 cup flour
2 1/2 cups whole milk
1 pound sharp cheddar cheese, coarsely grated (about 4 cups)
1 tablespoon dijon mustard
1 teaspoon hot pepper sauce
2 large eggs
1 pound penne pasta
Lightly butter a 15 by 10 inch baking dish.
Melt butter in a 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.
Heat oven to 400F. Bake pasta until cheese sauce is bubbling around edges, 25 to 30 minutes.
Recipe adapted from Bon Appetit, March 2009