Place the raw cashews in a bowl and pour boiling water over them. Let the cashews soak for 30 to 40 minutes. Drain and set aside.

Heat oven to 425°. Toss the tomatoes and onion in olive oil. Place them on a large sheet pan and spread them out in a single layer.

Cut about 1/4 inch off the top of the heads of garlic, exposing the individual cloves. Place the garlic heads, cut side up, on the baking sheet with the onions and tomatoes. Cover the garlic heads with a small sheet of tin foil. 

Sprinkle everything with salt and roast for 35 to 40 minutes until the tomato skins burst and become slightly charred. Depending on the size of the garlic, you may need to place the garlic back in the oven for an additional 5 to10 minutes until soft. Set aside when finished roasting.

In the meantime, cook the pasta according to the package directions. Reserve 1/2 cup of the water just before draining the pasta.

When the garlic has cooled enough to handle, squeeze the garlic heads until the cloves push out of their skins.

Add the roasted garlic and onions to a high powered blender. Toss in the soaked cashews, cashew vanilla unsweetened plant-based beverage, lemon juice and salt. Blend on high until smooth. Drizzle in olive oil and adjust salt to taste.

Pour the sauce into a large saucepan and heat over medium heat. Add the roasted tomatoes and cooked pasta. Stir in about 1/4 cup to 1/2 cup of the reserved pasta water. Stir in the raw spinach and cook until the spinach is wilted.

Serve hot with freshly grated nutmeg and parmesan cheese if desired.