Step 1In a 3-quart, heavy-bottom pot, heat the oil over medium-high heat and saute the onions, stirring often until soft, about 10 minutes. Stir in the garlic and potato and continue to cook just until the garlic is aromatic.
Step 2Add 5 cups of water and the bay leaves and bring to a boil. Season with a heaping teaspoon of salt and lower the heat slightly to maintain a good simmer. Cover and simmer for 15 to 20 minutes until the potatoes are just cooked through. Remove from the heat.
Step 3Bring a large pot of salted water to a boil, add the cabbage and simmer until tender, about 10 minutes. Set the pot aside.
Step 4With a slotted spoon, remove two large spoonfuls of potato from the pan (discard the bay leaves) and keep to the side. Puree the rest of the soup until smooth and return to low heat. Use your slotted spoon to add the cabbage to the pureed soup, together with about a cup of its cooking water. Allow to simmer for 5 minutes to meld the flavors, then add back the whole potato pieces. Adjust the seasoning with 1 teaspoon salt and one-fourth teaspoon pepper, or to taste, and remove from heat. Cover and keep the pan warm while you prepare the chorizo.
Step 5Grill the chorizo over a very hot grill or grill pan until golden and charred in places, then slice thinly. Ladle the soup into bowls and top each with a few slices of the sausage. Add a drizzle of piri piri sauce or oil.