Place the onion, carrot, celery and broccoli in a large pot. Add 6 cups water, basil and salt to the pot and stir. Bring to a boil over high heat then cover and reduce heat to a low simmer.: The pot will begin to steam and send up a green, slightly sweet aroma as the onion and carrot release moisture; you should hear a steady soft simmer once you reduce the heat, not a violent boil. This gentle simmer allows the flavors to meld without breaking down the vegetables too quickly, preserving some structure for later blending. Watch for a rolling steam and loosen the lid occasionally to prevent overflow, especially as the starches on the surface bubble. One common mistake is leaving the pot at too high a heat, which can reduce liquid too fast and leave the vegetables unevenly cooked.
Let simmer for 15 to 20 minutes or until broccoli is tender.: As the minutes pass you will notice the broth take on a pale green color and the texture of the broccoli soften; use a fork to test the stalks for fork tender doneness. The 15 to 20 minute window ensures the stalks lose their raw, fibrous quality while keeping the florets from becoming waterlogged. If you simmer much longer the flavors can become overly mellow, losing brightness, so check early and often. A typical slip up is assuming time alone guarantees tenderness; always test the vegetable pieces for the texture you prefer.
Meanwhile, in a blender, create your cashew cream. Blend together the cashews and remaining 1 cup water. (If you adjust the serving size, just keep the cashew to water ratio 1:1.): 1.) : When you blend the cashews with water you will see the mixture change from grainy to glossy, with a pale ivory color. The cream should pour slowly and coat the back of a spoon, indicating the right density. This step is crucial because the cashew emulsion contributes the soup's luxurious mouthfeel; blending too briefly leaves grit, while over thinning will reduce richness. A common error is using cold, very hard cashews straight from the jar without a short soak, which can stress the blender and leave a coarse texture.
Pour the cashew cream into the pot with the veggies and stir.: As you pour in the creamy mixture, the broth will lighten and develop a silkier sheen; stir gently so the cream distributes evenly through the hot liquid. This integration tempers the vegetal edge and binds the components into a cohesive soup base. Stirring too vigorously can incorporate air and change the texture, so fold the cream in with broad, gentle strokes. Beware of adding the cream while the pot is at a near rolling boil, which can cause frothing; slightly lower the heat if bubbling is vigorous.
Add the green lentils and stir again.: Introducing the cooked green lentils brings a soft nutty aroma and visible textural contrast in the pot, their muted color blending with the green broth. They absorb some of the flavored liquid and make the soup heartier, which is helpful if you want a meal in a bowl. Stir to ensure the lentils heat through evenly, and allow a few minutes for flavors to marry. A frequent oversight is adding undercooked lentils that need longer to soften, so always use fully cooked lentils or account for extra simmering time.
Add the spinach to the blender, and carefully (let the pot of veggies cool a bit first!) blend the soup in batches until smooth.: Adding the spinach to the blender with a portion of the simmered vegetables intensifies the color and fresh green flavor; as you blend, watch the sound change from churning to a smooth hum and the steam rise as the hot liquid emulsifies. The soup will turn a vibrant, uniform green and the texture will become velvety with no visible streaks. Blending in batches prevents overfilling the blender and reduces the chance of hot splatters. One safety mistake to avoid is blending a boiling hot full blender, always let the mixture cool slightly and vent the lid to prevent pressure build up.
Ladle into bowls, drizzle lightly with olive oil and top with freshly ground pepper, if desired. Enjoy!: The final presentation is important; when you ladle the soup you should notice a smooth surface with a glossy finish from the cashew cream. A light olive oil drizzle adds an aromatic top note and a slight richness on the palate, while freshly ground pepper gives a bright pop. Serve hot so the steam carries the aroma to your nose, and taste for final salt adjustments. Avoid over topping with oil or pepper which can mask the subtle green flavors you worked to develop.
