Heat ¼ cup of olive oil in a large pot over medium heat. Brown 285g of sliced chouriço for 3-5 minutes, then lift it out with a slotted spoon, leaving the fat.
Cook 1 large chopped Spanish onion with a pinch of salt until translucent, 5-7 minutes. Add 2 minced garlic cloves and cook for 2 minutes.
Add 6 medium Yukon Gold potatoes, peeled and chopped, and 8 cups of water. Bring to a boil, then simmer for 10-20 minutes, until the potatoes are almost tender.
Cool slightly and purée with an immersion blender. Stir in 450g of collard greens, stems removed and very thinly sliced, bring to a boil and simmer for 2-5 minutes, until tender.
Season with salt and pepper and top with the browned chouriço.
