In a 5 to 6-quart Dutch oven, melt 3 tablespoons of butter and 1 tablespoon of olive oil over medium heat. Wait for the butter to fully melt and start bubbling gently, about 2–3 minutes.

Add 2 roughly sliced large carrots, 1 cleaned and sliced leek, and 2 medium roughly sliced yellow onions to the pot, sprinkling them with kosher salt to taste. Cover and cook for approximately 10 minutes.

Stir in 3 minced garlic cloves and sauté for an additional 2 minutes.

Incorporate 4 large red skin potatoes cut into large pieces, and pour in 2 quarts of unsalted vegetable broth. Stir well and bring to boil, approximately 5–7 minutes.

Reduce heat to low and add 2 cups of broccoli florets if desired. Cover and let it simmer for 20 minutes.

Carefully blend the soup in batches using a countertop blender or a stick blender until smooth and creamy.

Return the blended soup to the pot and adjust seasoning with kosher salt and freshly ground black pepper before warming over low heat.

Serve the soup in bowls, garnished with freshly chopped chives and black pepper.