Add the sliced chouriço to a large heavy pot and set over medium-low heat. Cook, stirring occasionally, until the fat renders and the sausage edges are lightly browned, about 5–8 minutes.
Use a slotted spoon to lift out the chouriço and set aside in a bowl, leaving the rendered fat in the pot.
Add the diced bacon, onion, and sliced leeks to the pot with a pinch of salt. Cook over medium heat, stirring often, until they’re completely soft but not browned, about 8–10 minutes, so they melt into the base of the soup.
Stir in the minced garlic and cook for 1–2 minutes until fragrant. Then add the diced potatoes, diced turnips, bay leaves, bouillon cubes, and red lentils (if using), stirring to coat everything in the aromatics.
Pour in 2 liters (about 8½ cups) of water to start. Bring to a boil, then reduce to a gentle simmer. Cook until the potatoes, turnips, and lentils are very soft and starting to break apart, about 20–25 minutes.
Remove the bay leaves if using dried leaves, although wise leave in the fresh. Using a stick (immersion) blender, blend the soup directly in the pot until completely smooth and velvety. If it’s thicker than you like, add more water a cup at a time until you reach your preferred consistency; Caldo Verde should be thick but still sippable from a spoon.
Stir in the ground nutmeg (if using), then taste and season with freshly ground black pepper. Remember the bouillon, bacon, and chouriço are salty, so add salt gradually if you adjust the salt.
Add the thinly sliced collards or kale to the pot and bring the soup back to a gentle simmer. Cook just until the greens are tender but still bright, about 5–10 minutes, depending on how thinly they’re sliced.
Return the rendered chouriço (and any juices in the bowl) to the pot and stir through. Let the soup simmer for another 2–3 minutes so the flavors mingle, then taste again and adjust seasoning or water as needed.
Ladle into warm bowls, add a good drizzle of olive oil on top, and serve with a slice of broa de milho (Portuguese corn bread) or a good crusty bread for dunking; broa is the traditional partner for Caldo Verde and its dense crumb is perfect for soaking up the soup.