Classic Spaghetti Amatriciana | Share the Pasta

Ingredients

• 1 tablespoon extra virgin olive oil
• 8 ounces pancetta (thick cut, diced)
• 1 small white onion (finely diced)
• 3 large garlic cloves (finely minced)
• 2 tablespooons tomato paste
• 2 teaspoons dried red pepper flakes*
• 1 28-ounce can of crushed San Marzano tomatoes
• 3/4 ounce parmigiano-reggiano cheese (finely grated (plus more for serving))
• salt
• Freshly ground black pepper
• 1 lb dried spaghetti pasta
• 1 tablespoon unsalted butter