1. Heat a medium saucepan over medium heat. Swirl around the olive oil to coat the pan, and when the oil is hot, add the garlic and red pepper flakes. Stir constantly for 30 seconds, just long enough to release the garlic's fragrance and transform it slightly from its raw state. Don't cook it to golden.

2. Raise the heat to high and stir in the tomatoes and salt. Bring to a boil, reduce the heat, and simmer, uncovered, for 30 minutes. In the last 5 minutes of cooking, add the basil sprig, if using. Remove the basil before serving and swirl in the butter, if using.