1 (28-ounce) can whole peeled tomatoes
1 tablespoon extra-virgin olive oil
1 tablespoon unsalted butter
2 medium cloves garlic, minced
1 teaspoon dried oregano
Pinch red pepper flakes
Kosher salt
1 medium yellow onion, peeled and split in half
2 (6-inch) sprigs fresh basil with leaves attached
1 teaspoon sugar
Process tomatoes and their juice in food processor until puréed. Purée should not be completely smooth, but should have no chunks larger than 1/16th of an inch. Set tomatoes aside.
Combine oil and butter in medium saucepan and heat over medium-low heat until butter is melted. Add garlic, oregano, pepper flakes, and large pinch salt and cook, stirring frequently, until fragrant but not browned, about 3 minutes. Add tomatoes, onion halves, basil springs, and sugar. Bring to a simmer, reduce heat to lowest setting (bubbles should barely be breaking the surface), and cook, stirring occasionally, until reduced by half, about 1 hour. Discard onions and basil stems. Season to taste with salt.