Before you begin the rest of the prep work, place the cashews in a small bowl and cover them with very hot water. Set aside.
Heat the olive oil in a large Dutch oven over medium-high heat. Add the diced onion and cook until it has softened, 3-5 minutes. Stir in the curry powder and garlic and cook until fragrant, about 1 minute more.
Add the asparagus and broth and bring to a boil, then reduce the heat to low. Simmer uncovered until the asparagus has softened, about 15 minutes. Allow soup to cool slightly.
Rinse the cashews and put them in a blender with a ladle or two of the soup. Blend until completely smooth. Add the remaining soup to the blender (you may have to do this in batches) and puree until smooth and creamy; return to the Dutch oven and heat on medium until warmed through, then season with salt and pepper to taste. Serve with a squeeze of lemon juice.
Notes
If you have time, you can soak the cashews in cold water for 3-6 hours before using them.
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