Add the diced onion to the slow cooker, drizzle with olive oil, and turn it on low. Cook for about 15 minutes until the onion becomes translucent and fragrant, filling your kitchen with a sweet aroma.
Stir in the minced garlic and cook for another 2-3 minutes until the garlic releases its aroma and softens slightly, blending into the onion base.
Pour in the vegetable broth and turn the slow cooker to high. Cover and let the mixture simmer gently for about 30 minutes, allowing the flavors to meld and the onion to soften fully.
Add the fresh spinach all at once, pushing it beneath the liquid. Cover and cook for an additional 10-15 minutes, until the spinach wilts and turns a bright, vibrant green.
Use an immersion blender directly in the slow cooker to blend the soup until smooth and velvety, about 1-2 minutes. If you prefer some texture, blend only part of the soup.
Stir in the heavy cream (or coconut milk) and season with salt and pepper to taste. Warm the soup for another 2 minutes, then turn off the heat.
Spoon the hot, creamy soup into bowls, drizzle with a little olive oil, and serve immediately for a cozy, nourishing meal.
