1 pound fusilli, cooked just under al dente
1 teaspoon olive oil
1/4 pound pancetta, cut into 1/2-inch thick slices
1/2 yellow onion, minced
3 cloves garlic, minced
3 teaspoons fresh thyme, finely chopped
4 tablespoons unsalted butter
4 tablespoons all-purpose flour
4 cups whole milk
3 large egg yolks, lightly beaten in small bowl
1/2 teaspoon Dijon mustard
1 1/2 cups (6 ounces) Wisconsin Gruyere Cheese, shredded and divided
1 1/4 cups (5 ounces) Wisconsin Parmesan Cheese, grated and divided
Salt to taste
Freshly ground pepper to taste