Ingredients

The following ingredients have 8 Servings
  • 8 tablespoons unsalted butter
  • 2 large onions, thinly sliced
  • 4 pounds tomatoes, dice into 1/2-inch pieces
  • 1 teaspoon kosher salt, plus more to taste

Instruction

  • Melt the butter over medium heat in a large pot. Add the onion and cook gently, lowering the heat if necessary, until the onions are soft, about 15 minutes. (The onions should take on very little color, but if they brown a little, it’s fine.)
  • Add the tomatoes and salt to the pot and bring to a simmer over medium-high heat, stirring every so often to ensure the onion isn’t scorching on the bottom of the pan. (If you cover the pan for 2 minutes, the mixture will come to a boil more quickly.) Once the mixture is simmering, lower the temperature, so the mixture is gently bubbling—medium heat should do it. Simmer for about an hour, stirring occasionally until the mixture has reduced and feels somewhat thick as you run a spoon through it. Purée with an immersion blender or transfer mixture to a food processor or blender (taking care to hold the lid down tightly lest it blast off due to the steam) and purée until smooth. Taste. Add more salt to taste.
  • Once cool, transfer to storage containers and refrigerate for up to a week or freeze for months.