In a 6 to 8 quart, heavy bottomed saucepan, heat olive oil over medium heat. Add onion, celery, and garlic and sweat over medium heat until vegetables are translucent. Add veal, pork and pancetta and stir into vegetables. Brown over high heat, stirring to keep meat from sticking together. Add tomatoes, milk, and thyme and simmer over medium low heat for 1 to 1 1/2 hours. Season with salt and pepper to taste and remove from heat. Preheat oven to 375 degrees F. Bring about 6 quarts of water to a boil and add 2 teaspoons sea salt. Set up an ice bath next to the stove top. Roll pasta dough to thinnest setting on pasta machine. Cut the pasta into 20 (5-inch) squares and drop into boiling water. Cook for 1 minute, until tender. Drain well and refresh in the ice bath. Drain on towels and set aside. Butter or oil a casserole and place 4 pasta pieces on the bottom. Cover the pasta with 1/5 of the bechamel, and cover the bechamel with 1/5 of the bolognese. Repeat until all pasta and all sauces are used. Top with grated Parmesan and bake for 45 minutes or until top is golden brown and casserole is bubbling. Remove from oven, let stand for 15 minutes, slice and serve immediately.
Mound 3 1/2 cups flour in the center of a large wooden cutting board. Make a well in the middle of the flour and add the eggs and olive oil. Using a fork, beat together the eggs and oil and begin to incorporate the flour, starting with the inner rim of the well. As you expand the well, keep pushing the flour up from the base of the mound to retain the well shape. The dough will come together when half of the flour is incorporated. Start kneading the dough with both hands, using the palms of your hands. Once you have a cohesive mass, remove the dough from the board and scrape up and discard any leftover bits. Lightly reflour the board and continue kneading for 6 more minutes. The dough should be elastic and a little sticky. Wrap the dough in plastic and allow to rest for 30 minutes at room temperature. Roll or shape as needed.
In a medium saucepan heat the butter until melted. Add flour and whisk until smooth. Cook over medium heat until light and golden brown, about 6 to 7 minutes. Meanwhile, in a separate pan heat the milk until just about to boil. Add the milk to the butter mixture 1 cup at a time, whisking continuously until very smooth, and bring to a boil. Cook 30 seconds longer and remove from heat. Season with salt and nutmeg. Yield: 2 cups