Heat the oil in a soup pot and add the onion, potato, garlic, bay leaf, and marjoram. Sauté over high heat, stirring often, until the potato and onion begin to brown, about 12 minutes.
Add the tomato paste and cook for 1 minute.
Add the peppers, paprika, and 1 teaspoon salt. Pour in the water and scrape the bottom of the pot. Bring to a boil, then lower the heat and simmer, partially covered, for 25 minutes.
Remove the bay leaf and blend the soup until smooth. Taste for salt, season with pepper, and add a teaspoon or so of vinegar.
Serve with the croutons on top and a sprinkling of chopped marjoram.