One-Pot Sourdough Tomato Soup with Bread Croutons
A rustic Italian-inspired tomato soup made in one pot, built on a base of caramelized onions and garlic, enriched with crushed tomatoes and good broth, then finished with fresh basil and topped with crispy sourdough croutons. The bread toasts right in the same pot at the end, absorbing the soup's flavors while staying crunchy. Ready in about an hour, deeply satisfying, and perfect for a quiet lunch or casual dinner.
- Prep
- 15 min
- Cook
- 40 min
- Wait
- 5 min
- Total
- 1 hr
- Makes
- 4 servings (about 6 cups soup with croutons)
Steps
Before you start
- Read through the recipe—the croutons toast in the hot soup at the end, so timing is simple.
- Have fresh basil ready; add it at the very end so it stays bright green and fragrant.
- Use good sourdough bread (day-old is fine) and cut it into bite-sized cubes.
Toast bread cubes
- Cut the sourdough bread into ½-inch (1.3 cm) cubes.
- Set aside in a bowl.
- (If your bread is fresh, leave it uncovered on the counter for 30 minutes to dry slightly; stale bread gives better texture.)
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Tip: Day-old or stale sourdough works best—it won't dissolve into the broth.
Caramelize onions and garlic
- Heat the olive oil in a large heavy-bottomed pot (5–6 quart / 4.7–5.7 L) over medium heat for 1 minute.
- Add the sliced onion and a pinch of salt.
- Stir every 2–3 minutes until the onion is soft, golden, and fragrant, about 8–10 minutes.
- Do not let it brown deeply.
- Add the minced garlic and stir constantly for 1 minute until fragrant.
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Ready when: Onion is soft and uniformly golden; garlic is fragrant and light brown.
Tip: Stir regularly to prevent sticking. Medium heat ensures the onion caramelizes gently without burning.
Deglaze and add tomato paste
- Add the tomato paste and stir constantly for 1–2 minutes, coating the onions and garlic evenly.
- The paste will darken slightly and deepen in color.
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Ready when: Tomato paste is slightly caramelized and adheres to the onions.
Tip: This step builds flavor by toasting the paste slightly; don't skip it.
Add tomatoes and broth
- Pour in the crushed tomatoes (with juice) and the broth, stirring well to combine and scrape any browned bits from the bottom of the pot.
- Add the sugar to balance the acidity.
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Ready when: Liquid is well mixed; no lumps of tomato paste remain.
Tip: Scrape the bottom with a wooden spoon to deglaze and incorporate fond for deeper flavor.
Simmer the soup
- Bring the soup to a gentle simmer over medium heat.
- Once simmering, reduce heat to medium-low and let it simmer uncovered for 20 minutes.
- Stir occasionally to prevent sticking.
- The soup will reduce slightly and flavors will meld.
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Ready when: Soup bubbles gently; tomato flavor deepens and becomes less raw-tasting.
Tip: Medium-low heat prevents splattering and ensures even, gentle cooking.
Season and add basil
- Taste the soup and adjust seasoning with sea salt and black pepper to your preference.
- Stir in the torn fresh basil, reserving a few leaves for garnish.
- The basil will begin to soften and infuse immediately.
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Ready when: Basil is distributed throughout; soup is bright and fragrant.
Tip: Add basil only at the end to preserve its fresh color and peppery bite.
Toast croutons in the soup
- Increase heat to medium-high.
- Once the soup returns to a gentle boil, scatter the sourdough bread cubes over the surface and gently stir them in so they are just submerged.
- Let them toast and absorb the soup for 2–3 minutes, stirring frequently.
- The bread will soften on the outside but hold its shape inside, creating a pleasant textural contrast.
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Ready when: Bread cubes are mostly submerged, softened on the outside, and have absorbed some broth without dissolving.
Tip: Don't add the bread too early—it will break down. If bread is too soft, reduce time; if still too crispy, add 1 more minute.
Serve immediately
- Ladle the soup into bowls, making sure to distribute the bread cubes evenly.
- Garnish with reserved fresh basil leaves and grated Parmigiano-Reggiano if using.
- Drizzle with a small spoonful of good olive oil if desired.
- Serve hot.
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Tip: Serve immediately after adding the bread so it stays slightly crispy. Soup will continue to thicken as it sits.
Good to know
Tips
- Use San Marzano tomatoes if possible—they have fewer seeds and a cleaner, sweeter flavor than other canned varieties.
- For a silkier soup, blend part of it (about one-third to one-half) with an immersion blender after simmering, then stir the blended portion back in. Leave some chunks for texture.
- If your soup tastes too acidic after tasting, add a tiny pinch more sugar (¼ teaspoon / 1 g) rather than reaching for baking soda, which can create foam.
- This soup is a great way to use the last bits of fresh basil before frost; tear it roughly rather than cutting to prevent browning.
Make ahead
You can make the soup through step 6 (after simmering and adding basil) up to 2 days ahead. Cover and refrigerate. Reheat gently over medium-low heat until simmering, then add the fresh bread cubes at serving time for best texture and crunch.
Storage & reheating
Room temperature: not recommended due to perishability. Refrigerator: store soup (without croutons) in an airtight container for up to 3 days; croutons separately in an airtight container for up to 2 days to maintain crispness. Reheat soup gently over medium-low heat and add fresh croutons at serving time. Freezer: soup (without croutons) freezes well for up to 3 months in airtight containers. Thaw overnight in the refrigerator and reheat gently over medium heat. Make fresh croutons when serving.
Substitutions
- canned crushed tomatoes (San Marzano preferred) → Two 14.5 oz (411 g) cans diced tomatoes, or 2 lb (910 g) fresh ripe tomatoes, blanched, peeled, and crushed. Fresh or diced canned tomatoes will add a chunkier texture; you may need to simmer 5 minutes longer for flavors to develop. Reduce broth by ¼ cup (60 ml) if using fresh tomatoes due to extra liquid.
- sourdough bread, day-old or slightly stale → Ciabatta, focaccia, or crusty white bread, day-old. Any crusty artisan bread works; sourdough's tang pairs beautifully with tomato but isn't essential. Avoid soft sandwich bread, which will dissolve.
- fresh basil leaves → 2 tablespoons (8 g) fresh oregano, or 1 teaspoon dried oregano (add during simmering, not at the end). Oregano will give an earthier, more herbal flavor than basil's peppery sweetness. Adjust to taste.
- vegetable or chicken broth, unsalted → 4 cups (960 ml) water plus 1 vegetable or chicken bouillon cube, or homemade broth. Store-bought broth is convenient; homemade adds richer depth. Taste before adding salt, as bouillon cubes are already salted.
