Blend  ¼ cup cashews and ¼ cup water until completely smooth. Set aside.

Set a colander or fine-mesh sieve over a large bowl. Drain butter beans, reserving the bean liquid. Set beans and bean juice aside.

In a large skillet over medium heat, add the olive oil, shallot and ½ tsp. salt; cook, stirring frequently, until softened, about 3 minutes. Add garlic and cook until fragrant, about 1 minute. Lower heat slightly. Add cashew cream, water, lemon zest, reserved beans, and ¼ cup reserved bean liquid. Bring to a gentle simmer and cook, stirring occasionally, until liquid is reduced by about half, 4-5 minutes. Stir in lemon juice, then fold in the spinach and cook until wilted, 1-2 minutes. Season with pepper and remaining salt as needed. If the sauce is too thick, add 1-2 Tbsp. water to reach desired consistency. 

Serve as is, or over a bed of rice or your favorite grain and enjoy!