For the lentils: Remove the outer layers from the head of garlic and cut off about 1/4 inch of the stem end to expose the cloves. Add the lentils to a large pot and cover them by 2 inches with water. Add the onion, carrots, celery, bay leaf, the head of garlic and a couple of pinches of salt. Bring the lentils to a boil over high heat, reduce the heat to a simmer and cook until the lentils are creamy and tender, about 40 minutes.
Remove and discard the onion, carrots, celery, bay leaf and garlic. Using an immersion blender, puree about one-third of the lentils and return them to the pot. (Or scoop one-third of the lentils into a standard blender and puree, then add back to the pot.)
For the soffrito: In a food processor, combine the red onion, carrots, celery, rosemary and thyme and pulse until the vegetables are minced. Add the mixture to a separate large soup pot along with the olive oil. Turn the heat to high and fry the vegetables, stirring occasionally, until they soften and color slightly, 10 to 12 minutes. Add the tomato paste, canned tomatoes with their juice, and a couple pinches of salt to the soffrito and stir. Reduce the heat to medium-high and cook for 10 minutes. Add the kale and another pinch of salt, stirring to coat the leaves. Reduce the heat to medium and cook for 10 minutes, until the kale is soft.
Add the lentils into the pot of vegetables and stir. Add about 2 cups water, a little at a time, to thin the soup (it can be more or less water, depending on the level of thickness you prefer). Increase the heat to high and bring to a boil. Reduce the heat and simmer for about 30 minutes to allow the flavors to come together. Taste and add salt, if needed. Serve with black pepper, Parmesan and a drizzle of olive oil.