Soak the pinto beans overnight. After the beans are soaked, drain the soaking water and rinse them well.
Peel and slice the onion, and chop the potatoes, carrots, and tomatoes.
Place a pot over medium heat and add the olive oil.
Add the onions to the pot. Keep stirring and fry them until they are brown and soft.
Add the beans, potatoes, carrots, and onion to the pot and cover with water.
Bring to a boil and once it starts boiling reduce the heat to low. Let it simmer for about an hour.
Check if the ingredients are soft and cooked.
When it is cooked, take an immersion blender and blend until the soup becomes homogenous.
Add salt and pepper to taste.
Wait a few minutes for the soup to cool down.
Serve with slices of sourdough bread.