Preheat the oven. Arrange a rack in the middle of the oven. Heat the oven to 400ºF/204ºC
Roast the vegetables. Add all the vegetables to a baking sheet, drizzle with oil, sprinkle with salt, and toss to coat. Spread all the vegetables into a single layer so they roast evenly and brown at the edges and roast until the carrots are tender when pierced with a fork and the vegetables begin to brown slightly, for about 35 minutes, tossing the vegetables halfway through roasting.
Simmer. First, remove the garlic cloves from their skins. Then, transfer the roasted vegetables to a large pot, add the rosemary and bay leaf, cover everything with vegetable broth, and bring it to a boil over high heat. Turn the heat off, cover the soup with a lid, and let it sit for 15 minutes. Blend. Add the roasted vegetables, vegetable broth, and lemon juice to a high-speed blender and blend on high until smooth. I love rosemary, so I typically blend some rosemary leaves as well. If your soup is too thick, add up to 1 cup/240 ml more broth and blend. I recommend starting with less broth and adding more as needed - you can always add more to thin the soup out, but you can't take it out if you add too much at first. Serve immediately, straight out of the blender.
Blend. Add the roasted vegetables, vegetable broth, and lemon juice to a high-speed blender and blend on high until smooth. I recommend starting with less broth and adding more as needed - you can always add more to thin the soup out, but you can't take it out if you add too much at first.
Season. Taste and adjust the flavor as needed, adding more salt for saltiness and lemon juice for acidity.
Serve. Pour the soup into serving bowls - it will be hot straight out of the blender. Garnish with a freshly chopped parsley and a sprinkle of black pepper.
Store. Leftover soup keeps well covered in the refrigerator for 3-4 days. For longer-term storage, freeze in an airtight container for up to 3 months.
Reheat. Transfer frozen soup into the refrigerator 24 hours before reheating to thaw slightly. Reheat in a pot on the stovetop over medium-low heat, stirring frequently, until hot. Add ¼ cup/60 ml water/broth at a time if too thick.