How to Make It
Preheat oven to 375°F. Toss together cauliflower, curry powder, and 2 tablespoons of the oil in a bowl; spread in a single layer on a rimmed baking sheet. Roast, stirring halfway through cook time, until tender and lightly browned, about 45 minutes.
Meanwhile, heat remaining 1 tablespoon oil in a medium saucepan over medium. Add onion; cook, stirring occasionally, until softened, about 6 minutes.
Add roasted cauliflower, stock, cashew milk, nutritional yeast, and salt to onion in saucepan; bring to a boil over medium-high. Remove from heat. Using an immersion blender, process mixture in saucepan until smooth, about 30 seconds (or transfer to a blender and blend until smooth).