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

Add garlic and flour

Add the minced garlic and cook 30–45 seconds until fragrant. Sprinkle the flour over the vegetables and stir constantly for 1–2 minutes to cook the raw flour taste and create a light roux.

Deglaze and add stock

Slowly pour in about 1 cup of the stock while stirring to deglaze the pot and incorporate the roux. Add the remaining stock, the bay leaf, thyme sprigs, diced potato (if using), salt and pepper. Bring the mixture to a gentle boil, then reduce heat to a simmer.

Simmer

Simmer the soup gently, uncovered or partially covered, for 20–25 minutes, until vegetables and potato (if used) are tender and flavors have melded.

Add-ins / Finish

Add tomatoes and protein

If using diced tomatoes and/or cooked chicken or beans, stir them into the simmering soup and heat through for 5–7 minutes.

Add greens

Add the chopped spinach or kale and cook 2–4 minutes until wilted and tender.

Finish with cream and herbs

Remove and discard the bay leaf and thyme stems. Stir in the heavy cream or coconut milk (if using) and fresh lemon juice. Taste and adjust seasoning with additional salt and pepper as needed. Stir in chopped parsley.

Serve

Ladle soup into bowls, sprinkle with grated Parmesan if desired, and serve hot with crusty bread.