In a large heavy-bottomed pot or Dutch oven, warm the olive oil and butter over medium heat until the butter melts and foams. Add the diced onion, carrot, and celery (mirepoix) and a pinch of salt. Cook, stirring occasionally, until the vegetables are soft and translucent, about 6–8 minutes.

Add garlic

Add the minced garlic and cook for 30–45 seconds until fragrant, being careful not to brown it.

Vegetables & Protein

Brown mushrooms and add firmer vegetables

Increase heat to medium-high. Add the sliced mushrooms and cook for 3–4 minutes until they release liquid and begin to brown. Add the diced potato and zucchini and stir to combine; cook for 2 minutes to coat with the aromatics.

Add beans and any cooked protein

Stir in the drained cannellini beans and shredded cooked chicken (if using). Let them warm for 1–2 minutes before adding liquids.

Liquids & Seasoning

Deglaze and build the soup

Stir in the tomato paste and cook 1 minute to remove raw flavor. Pour in the stock and water, scraping any browned bits from the bottom of the pot. Add the dried thyme, oregano, bay leaf, kosher salt, and black pepper. Bring the soup to a gentle simmer.

Simmer until vegetables are tender

Reduce heat to maintain a gentle simmer and cook uncovered for 15–20 minutes, until potatoes are tender when pierced with a fork and flavors are blended. Taste and adjust seasoning, adding up to 1/2 tsp more salt if needed.

Finishing & Garnish

Finish with brightness and herbs

Remove the bay leaf. Stir in the lemon juice and chopped parsley. If using red pepper flakes or Parmesan, add now to taste. For a slightly creamier texture, mash a cup of the soup against the side of the pot with a spoon and stir back in, or pulse 1–2 cups in a blender and return to the pot.

Serve

Ladle the soup into bowls and garnish with additional parsley and grated Parmesan if desired. Serve hot with crusty bread.