Heat a large saucepan over medium heat and add olive oil or butter, allowing it to melt and warm up until it releases a faint nutty aroma.
Add the diced yellow onion and minced garlic to the pan. Cook, stirring frequently, until the onion becomes translucent and fragrant, about 2-3 minutes, with a gentle sizzling sound.
Toss in the fresh spinach and stir until it wilts down, releasing a bright, earthy aroma as it reduces in volume, about 2 minutes.
Pour in the vegetable broth and bring the mixture to a gentle simmer. Reduce the heat to low and let it cook uncovered for about 10 minutes, allowing the flavors to meld and the greens to soften further.
Once simmered, carefully transfer the hot mixture to a blender. Puree until smooth and velvety, about 30 seconds, being cautious of the hot liquid.
Return the pureed soup to the saucepan and stir in the heavy cream and a pinch of nutmeg. Warm gently over low heat for 3-5 minutes, until the soup is silky and well combined. Add salt and pepper to taste.
Squeeze in the fresh lemon juice and stir to brighten the flavor, then taste and adjust seasoning as needed.
Ladle the hot soup into bowls, garnish with an extra drizzle of cream or a few fresh spinach leaves if desired, and serve immediately for a comforting, velvety experience.
