Peel and chop the potatoes into small, even cubes to help them cook quickly and uniformly.
Heat a large pot over medium heat and add a tablespoon of olive oil until shimmering and fragrant.
Add the chopped onion to the pot and sauté until translucent and soft, about 5 minutes, until you start to smell a sweet aroma.
Stir in the minced garlic and cook for another minute until fragrant, watching for a warm, pungent aroma filling the kitchen.
Add the cubed potatoes to the pot, stirring to coat them with the aromatics, and cook for 2-3 minutes.
Pour in the vegetable broth, ensuring the potatoes are just covered, then turn up the heat to bring everything to a gentle boil.
Reduce the heat to low and let the soup simmer uncovered until the potatoes are fork-tender, about 15-20 minutes.
Use an immersion blender directly in the pot or carefully transfer the soup to a blender in batches, blending until the mixture is smooth and velvety.
Return the smooth soup to the pot if needed, then stir in the plant-based milk and lemon juice, adjusting the amount for your preferred creaminess and brightness.
Season with salt and pepper to taste, then simmer for another 5 minutes to meld flavors.
Taste the soup and adjust the seasoning if necessary, adding more lemon juice or salt for balance.
Serve the soup hot, garnished with fresh herbs or a drizzle of olive oil if desired, and enjoy its creamy, comforting texture.