Chop your veg: Start by chopping the onion and zucchini. No need to be too precise—it’s all getting blended later!
Heat your pan: In a large pot, heat the olive oil and butter over medium heat until the butter is melted and bubbly.
Sauté the aromatics: Add the chopped onion and cook for 3–4 minutes, until soft and translucent. While that’s cooking, prepare your garlic (about 2–3 cloves, or to taste).
Add the garlic: Stir in the garlic and cook for another minute until fragrant—don’t let it brown!
Simmer the zucchini: Add the chopped zucchini and enough water to just cover the veggies (about 3–4 cups). Cover the pot and let everything simmer for about 15 minutes, or until the zucchini is soft.
Add the basil: Once the zucchini is tender, stir in a generous handful of fresh basil, and season with salt and pepper to taste.
Blend until smooth: Carefully blend the soup using an immersion blender, or transfer to a blender in batches. Blend until creamy and smooth.
Serve it up: Ladle into bowls and enjoy as is, or top with a swirl of olive oil, a dollop of yogurt, more basil, or even crunchy seeds.