Caldo Verde (Portuguese Green Soup)

Name: Caldo Verde (Portuguese Green Soup)
Prep time: 30 min
Cook time: 45 min
Total time: 1 h 15 min
Cuisine: Spanish, Portuguese
Ingredients: 4 tablespoons olive oil, divided; 1 medium onion, minced; 1 clove garlic, minced; 6 medium potatoes, peeled and thinly sliced; 2 quarts cold water; 6 ounces linguiça sausage, thinly sliced; 2.5 teaspoons kosher salt; ground black pepper to taste; 1 pound kale, rinsed and julienned