Like many of the "classic" Italian dishes, there are many variations on this one too.
Here's the one I was shown in southern Italy were it was supposed to have originated.
We can also debate the origin of the name.

Ingredients:
  • 2 C - San Marzano Tomatoes (DOP) - whole and with juices
  • 1 Onion - Large dice
  • 1 tsp fresh thyme
  • 1 tsp fresh oregano
  • 2 Garlic cloves - Crushed but whole
  • 1 cup of oil-cured Green Olives - chopped
  • 2 Tbs salt packed capers - fully rinsed and drained
  • 1/4 tsp - Hot red pepper flakes or to taste - This is traditionally a "hot" dish.
  • 2 or 3 Tbs Extra Virgin Olive Oil
  • 2 fillets of salt packed anchovies - soaked in water or milk and chopped
Method:

Heat the oil in a good size sauté pan or skillet.
Add the anchovies and whole garlic cloves.
Cook until garlic browns lightly and the anchovies break apart.
Add the red pepper flakes and cook a few seconds more.
Add the tomatoes, olives, and capers.
Simmer for 30 minutes.
Because of the anchovies, olives and capers, Do not add salt until you've tasted the finished sauce.
Serve over a string pasta. Spaghetti is traditional.