In 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. Cook, stirring occasionally, until vegetables are softened and translucent, about 6–8 minutes.

add garlic and flour

Add the minced garlic and cook 30 seconds until fragrant. Sprinkle the flour over the vegetables and cook, stirring, 1–2 minutes to remove raw flour taste and form a light roux.

deglaze and add liquids

Slowly whisk in 1 cup of the stock to loosen the roux, scraping any browned bits from the pot. Gradually add the remaining stock while whisking to prevent lumps. Add the diced potato (if using), dried thyme, bay leaf, kosher salt and pepper. Bring to a gentle simmer.

Protein and vegetables

cook chicken or mushrooms

If using chicken: add the diced chicken to the simmering broth and cook until the pieces are opaque and cooked through, about 6–8 minutes. If using mushrooms: sauté mushrooms in a separate skillet with 1 tsp olive oil until golden, then add to the pot.

finish vegetables

Add the frozen peas and chopped spinach or kale to the pot in the last 2–3 minutes of cooking so they only need to heat through and retain color and texture.

Finish & serve

creamy finish

Reduce heat to low. Stir in the milk or half-and-half and warm through gently for 2–3 minutes; do not boil vigorously after dairy is added to prevent splitting. Taste and adjust seasoning with additional salt and pepper if needed.

brighten and garnish

Remove and discard the bay leaf. Stir in chopped parsley and lemon juice if using. Ladle soup into bowls and serve hot with crusty bread or crackers.