Begin by heating a drizzle of olive oil in a medium pot over medium heat. Add the chopped onion and sauté for 5 to 7 minutes until translucent and fragrant, stirring occasionally to avoid browning.

Toss in the fresh spinach and stir until it begins to wilt, about 2 minutes. Add the drained white beans and pour in the vegetable broth, stirring gently to combine.

Raise the heat to bring the soup to a gentle simmer. Let it cook uncovered for about 10 minutes to allow the flavors to meld. Remove from heat and use an immersion blender to puree the soup until smooth and creamy. Alternatively, transfer the mixture in batches to a blender, being cautious with the hot liquid.

Season with salt, freshly ground black pepper, and a pinch of red pepper flakes for a subtle kick. Stir once more, taste, and adjust seasoning if needed. Serve hot, garnished with a swirl of olive oil or a sprinkle of chili flakes if desired.