Boil the pasta: Bring a large pot of salted water to a boil. Cook pasta until just al dente according to package directions. Reserve 1 cup pasta water, then drain.

Sauté aromatics: While the pasta cooks, warm olive oil in a large skillet over medium heat. Add the onion with a pinch of salt and cook 4–5 minutes until softened. Stir in garlic and cook 30–60 seconds, until fragrant.

Build the tomato base: Stir in tomato paste and cook 1 minute to caramelize slightly. Add crushed tomatoes, vegetable broth, a pinch of salt, black pepper, and red pepper flakes if using. Simmer 6–8 minutes, stirring occasionally.

Make it creamy: Reduce heat to low. Whisk in the cashew or almond milk until smooth. Let it gently bubble for 2–3 minutes to thicken slightly.

Temper the yogurt: In a small bowl, whisk Greek yogurt. Add a few spoonfuls of the warm sauce to the yogurt and whisk again. Then stir the tempered yogurt into the skillet. This keeps the sauce silky and prevents curdling.

Season and brighten: Add balsamic vinegar and taste. Adjust salt, pepper, and vinegar until balanced. If you like, add lemon zest for a fresh lift.

Add greens and basil: Fold in baby spinach and cook 1–2 minutes until wilted. Stir in most of the basil, saving some for garnish.

Toss with pasta: Add cooked pasta to the skillet and toss to coat, adding reserved pasta water a little at a time until the sauce clings to the noodles and looks glossy.

Finish and serve: Top with remaining basil and a sprinkle of Parmesan if you’d like. Serve warm.