Heat the olive oil in a large pot over medium heat. Once shimmering, add the diced onion. Sauté for about 5 minutes until the onion becomes translucent and fragrant.

Add the minced garlic and chopped celery. Continue cooking for another 2 to 3 minutes, stirring frequently.

Pour in the vegetable broth and add the cubed potatoes. Increase the heat and bring everything to a boil, then reduce to a gentle simmer.

Let the soup simmer for 15 to 20 minutes until the potatoes are fork-tender.

Remove from heat and add the fresh basil leaves, lemon juice, and lemon zest. Stir to combine.

Use an immersion blender to puree the soup until smooth, or transfer to a countertop blender in batches.

If using heavy cream, stir it in now and warm through on low heat. Season with salt and black pepper to taste.

Ladle into bowls and garnish with extra basil leaves, a drizzle of olive oil, or a swirl of cream. Serve immediately.