Begin to boil the potatoes in a pot until a fork and slide through them with ease. Once the potatoes are done, drain them and set aside.

Meanwhile, heat the olive oil and butter in a stock pot or Dutch oven over medium heat. Add the carrots, celery, and onions and season with salt and pepper. Cook until soft, but not brown, about 10 minutes.

Add in the leeks and cook until they are soft, about 2-3 minutes.

Next, add in the parsley, basil, and spinach and stir in with the other vegetables. Once the spinach is wilted, add in the beef bones, potatoes, and water. Be sure to season with salt and pepper.

Raise the heat to high to bring the soup to a boil. Then immediately lower it to a simmer and continue to cook for another 15 minutes.

Remove the beef bones and discard them at this point.

Use an immersion blender to blend the ingredients together. Be sure not to over-blend as the potatoes will become paste-like.

Alternatively, if you do not have an immersion blender, you can use a standard blender or food processor. You will also need a ladle and a second pot and will work in batches. Ladle some of the soup into the blender. After blending each batch, pour it into the second pot. Repeat this process until everything is blended.

Return the pot to the heat. Taste the soup and make any adjustments to the salt. Cook for another 10 minutes to thoroughly incorporate all the flavors together.

Serve as is or with sour cream or goat cheese.