Melt the Butter: Add the butter to a large saucepan or Dutch oven and melt it over medium heat until fully liquid and starting to sizzle.
4 tablespoons unsalted butter
Combine Everything: Add the onion wedges, canned tomatoes with their juices, water or broth, and salt to the pot. Stir gently to combine.
½ large onion, 1 28-ounce can whole peeled or crushed tomatoes, with juices, 1 ½ cups water, ½ teaspoon salt
Simmer Gently: Bring everything to a gentle simmer. Cook uncovered for 40 minutes, stirring occasionally. The onion will soften, the tomatoes will break down, and the whole thing will smell like comfort in a pot.
Blend the Soup: Turn off the heat and blend the soup until smooth. An immersion blender makes this super easy, but a regular blender works too—just blend in batches and be careful with the hot liquid.
Taste and Adjust: Give the soup a taste and add more salt if needed. Leave it a little chunky or make it silky smooth—it’s your call.
Store the Leftovers: Let the soup cool completely, then store it in an airtight container. It’ll keep in the fridge for 3 days or in the freezer for up to 3 months.