Dice the onion and mince the garlic cloves fresh (this makes a noticeable difference in flavor compared to pre-minced). Heat the avocado oil in a large pot over medium heat until it shimmers, about 1 minute. Add the diced onion and cook, stirring occasionally, until it becomes translucent and softened, about 3 minutes. This develops a sweet flavor foundation for the soup.

Add the minced garlic and Italian seasoning to the softened onion and cook for 1 minute, stirring constantly, until fragrant. This blooming technique releases the essential oils from the seasonings. Stir in the tomato paste and cook for another 3 minutes, allowing it to caramelize slightly in the oil—this deepens the savory flavor of the entire soup and prevents it from tasting thin or watery.

Pour in the diced tomatoes with their juice and the stock, stirring well to incorporate the tomato paste. Season with a generous pinch of salt and black pepper to taste. Increase the heat to medium-high and bring the soup to a boil, then add the tortellini and cook for 6 minutes, stirring occasionally to prevent sticking. The tortellini will cook perfectly in the simmering broth while you prepare the creaminess element.

While the tortellini cooks, whisk the cashew butter together with 1 cup of water in a small bowl until completely smooth and combined (I find whisking vigorously for about 30 seconds creates the creamiest result). This cashew mixture adds richness and body to the soup while keeping it completely dairy-free, creating that luxurious mouthfeel you'd expect from a creamy soup.

Stir the cashew butter mixture from Step 4 into the simmering soup, whisking gently to distribute it evenly and prevent lumping. Add the nutritional yeast for a savory umami boost that enhances the tomato flavors. Finally, add the fresh spinach and stir until it wilts completely, about 1 minute. Taste and adjust seasoning with additional salt and pepper as needed.

Ladle the soup into bowls immediately while hot. The tortellini should be tender, the broth rich and creamy, and the spinach vibrant. This soup is best served right away to enjoy the fresh spinach and the perfect texture of the tortellini.