Heat the olive oil in a soup pot over medium heat, then add the onion and a pinch of salt and sauté until translucent and golden, about 5 minutes. Add the garlic and sauté for 2 minutes more. Stir in the carrots, parsnips, cinnamon, red pepper flakes, thyme and 1/4 teaspoon salt and sauté until well combined. Pour in the broth and cook until the carrots and parsnips are tender, about 15 minutes. In a blender, puree the soup in batches until very smooth, each time adding the cooking liquid first and then the carrot mixture. If needed, add additional broth to reach the desired thickness. Return the soup to the pot over low heat, stir in the lemon juice, maple syrup, and a pinch of salt, and gently reheat. Adjust to taste.