Heat a large heavy-bottomed pot over medium heat. Add the olive oil and butter. When butter is melted and foaming, add the diced onion, carrots and celery. Sauté, stirring occasionally, until the onion is translucent and the carrots begin to soften, about 6–8 minutes. Add the minced garlic, dried oregano, thyme sprigs and bay leaf and cook 1 minute until fragrant.

Vegetables & Protein

Add vegetables and optional chicken

Add the diced potatoes and zucchini to the pot and stir to coat with the aromatics. If using chicken, add the diced chicken now and cook, stirring occasionally, until the exterior is just opaque, about 3–4 minutes.

Stir in the canned diced tomatoes with their juices, corn kernels and rinsed cannellini beans. Mix well so the beans and vegetables are distributed evenly.

Liquid & Seasoning

Add stock and simmer

Stir in the tomato paste, then pour in the chicken or vegetable stock and 1 cup water. Bring the soup to a gentle boil over medium-high heat, scraping up any browned bits from the bottom. Taste and add kosher salt, black pepper and red pepper flakes (if using). Reduce heat to low and simmer, uncovered, until the potatoes are tender and flavors meld, about 18–22 minutes.

Finishes & Garnish

Remove and discard the thyme sprigs and bay leaf. If you prefer a slightly creamier texture, use an immersion blender to purée 1 to 2 cups of the soup and stir back in (or transfer 1–2 cups to a blender, purée and return). Stir in the chopped parsley and lemon juice. Adjust seasoning with additional salt and pepper to taste.

Ladle the soup into bowls and finish with freshly grated Parmesan if desired. Serve hot with crusty bread.