- Cook pasta in a large pot of boiling salted water 1 to 2 minutes less than package instructions. Drain, rinse with cool water and return to pot.
- Meanwhile, heat 4 tablespoons butter in a medium saucepan over medium-high heat. Add flour; cook, whisking, 1 minute. Add milk, cayenne, nutmeg and 2 teaspoons salt; bring to a simmer. Cook, whisking, until mixture is thick enough to coat the back of a spoon, 2 to 3 minutes. Whisk in cheeses until smooth. Pour over pasta; toss to coat. Divide among baking dishes.
- Melt remaining 2 tablespoons butter, toss with breadcrumbs. Sprinkle over pasta. Bake uncovered at 350F until golden and bubbling 20 to 30 minutes.
- Or cover tightly with plastic wrap; freeze up to 3 months. Place frozen dishes on a baking sheet; remove plastic. cover with foil and bake until bubbling 60 to 70 minutes. Remove foil; continue baking until golden 5 to 10 minutes more.