Spaghetti Bolognese

Ingredients

• 1 tablespoon extra-virgin olive oil
• 1/2 onion, finely diced (1/2 cup)
• 1 carrot, finely diced
• 2 celery stalks, finely diced
• 4 ounces pancetta, finely diced (optional)
• 1 pound ground beef, or a combination of beef and pork
• coarse salt
• 1/2 cup red or white wine
• one 28-ounce can best-quality tomatoes, pulsed in a blender
• 1/2 cup cream or milk
• freshly ground black pepper
• 1/4 teaspoon crushed red-pepper flakes
• 1 pound spaghetti or other pasta
• 1 1/2 tablespoons unsalted butter
• 1/2 cup freshly grated parmesan cheese