Heat a large dutch oven or large stock pot over medium-high heat. Add 1-2 tablespoons of oil, along with the onion. Cook for 2-3 minutes, until softened. Then, reduce the heat to medium and stir in 2 ½ tablespoons white miso before adding 2 stalks celery, 1 bulb fennel, 3 cloves garlic, 1 tablespoon thyme leaves, and 1 teaspoon oregano. Continue to saute for 2 more minutes. Add the 2 cubed potatoes, 6 ½ cups stock, ⅓ cup lentils, 1 teaspoon sea salt, and season with black pepper.

Cover and cook for 15 minutes. Then, check to see if the lentils are done cooking. If not, cover and cook for 5-10 minutes more until the lentils are tender and cooked through.

Taste everything and adjust salt and pepper to your liking.

Add the eggs to a small bowl and whisk until frothy and slightly lighter in color. Then add the lemon juice and whisk to combine well. To temper the eggs, slowly add three tablespoons of hot broth into the lemony egg mixture, whisking constantly.

Very carefully, add the egg mixture to the soup, whisking constantly until combined. Reduce the heat to low and cook, continuing to stir constantly, until the soup is thick enough to lightly coat the back of a spoon. This should take approximately 5 minutes. Do not let the soup reach a simmer.

Add the spinach leaves right before serving so that they wilt into the soup.

Let the soup cool slightly and then ladle into bowl and top with reserved fennel fronds and/or crumbled cheese.