Roast the Asparagus: Preheat your oven to 425°F (220°C). Trim the ends off of the asparagus with a sharp chef’s knife. Arrange the asparagus on a baking sheet. Drizzle with 2 tablespoons of olive oil and season with salt and pepper. Toss to coat evenly. Roast in the preheated oven for about 15-20 minutes or until the asparagus is tender and starts to caramelize, turning once halfway through. Set aside a few tips for garnish if desired.
Sauté the Aromatics: As the asparagus is roasting, heat the remaining 1 tablespoon of olive oil over medium heat in a large soup pot. Add the onion and a pinch of salt, cooking until the onion is soft and translucent, about 5 minutes. Add more oil if required. Add the garlic and cook for another minute until fragrant.
Prepare the Soup: Cut the roasted asparagus into 1-inch pieces and add them to the pot with the onions and garlic. Pour in the bone broth and bring the mixture to a simmer. Let it cook for about 10 minutes, allowing the flavors to meld.
Blend the Soup: Using an immersion blender, blend the soup until smooth. Alternatively, you can use a regular blender, working in batches if necessary. Be careful when blending hot liquids. Return the soup to the pot if you used a regular blender.
Finish the Soup: Stir in the heavy cream, lemon zest, and juice. Bring the soup to a gentle simmer, then add the fresh thyme. Adjust the seasoning with more salt and pepper as needed. If the soup is too thick, you can thin it with a little more bone broth or water until you reach your desired consistency.
Serve: Ladle the soup into bowls. Garnish with the reserved asparagus tips, a sprinkle of fresh thyme, and any optional toppings like a dollop of crème fraîche or sour cream, grated Parmesan, a poached egg, or crispy bacon bits.