Ingredients
2 tablespoons extra-virgin olive oil
1 cup minced sweet onion, such as Vidalia
Kosher salt
1 tablespoon minced garlic (from 2 to 3 cloves)
1/4 teaspoon red pepper flakes
2 cans (each 28 ounces) whole peeled tomatoes in juice, puréed
2 tablespoons unsalted butter
Preparation
Heat oil in a pot over medium-high. When it shimmers, add onion; season with 1 tablespoon salt. Cook, stirring occasionally, until soft and golden in places, 8 to 10 minutes (if onion colors too quickly, reduce heat to medium). Stir in garlic and red-pepper flakes; cook until fragrant, about 30 seconds.
Add puréed tomatoes and bring to a boil. Reduce heat to medium-low and simmer, stirring occasionally, until sauce is thickened slightly and reduced to 6 cups, 20 to 25 minutes. Remove from heat and stir in butter until melted and sauce is uniform in color. If not using it immediately, let the sauce cool to room temperature, then refrigerate it in an airtight container for up to five days, or freeze for up to three months.
