Combine the cashew butter, vegetable broth, garlic powder and nutmeg in a large bowl or saucepan. Microwave for 3 minutes on medium-high or cook over medium-high heat on the stove until it thickens (5-7 minutes). Whisk until fully combined.
Cut the onion in half and into thin slices. Wash the spinach.
Heat a pan with a little vegetable oil. When hot, sauté the spinach until wilted.
Roll out the pizza crust on parchment paper. Prick the bottom with a fork and fold the edges over (see step-by-step pictures in post above).
Spread a generous layer of white pizza sauce onto the crust. Top with the sauteed spinach and red onion. Drizzle some more white sauce on top.
Bake for 25-30 minutes (or according to package directions if using a store-bought crust).
Garnish with some fresh lemon, lemon zest and red pepper flakes if desired.
Notes
Use raw cashew butter, which is very light in color versus brown, roasted cashew butter. Jiva and Artisana are my favorite brands. Do not replace it with another type of nut or seed butter.
If you don't have cashew butter, soak ¾ cup of raw cashews in warm water for 2 hours. Drain them. Blend the soaked cashews with ¼ cup of vegetable broth, garlic powder and nutmeg in a high-speed blender until perfectly smooth. Add more water as needed.
For the vegetable broth, I love mixing water with bouillon powder to have just the right amount needed.
If using frozen spinach, let it defrost in a fine-mesh sieve over the sink. Once defrosted, press out excess moisture.
Freezing: this vegan white pizza sauce doesn't freeze well. We recommend making it shortly before serving as you can whip it up within minutes. You could however make up to 3 days ahead of time and store it in an airtight container in the refrigerator.