In a large pot, over medium-high heat, saute onion and garlic with 1 tbsp. olive oil until fragrant, about 1 minute. Add potatoes, diced tomatoes, vegetable broth/stock, water, tomato paste, and tomato sauce to the pot. Stir to mix together. Bring to a simmer then lower heat to medium-low. Cover and let simmer for 20-25 minutes, or until potatoes are fork-tender.
Uncover and stir in the kale until wilted. Season soup with salt and pepper, to taste.