- Preheat oven to 425°F.
- Combine cauliflower and leeks on a parchment-lined baking sheet. Drizzle with olive oil and toss with your hands to mix. Sprinkle with salt and pepper and roast for 20 minutes, stirring halfway through.
- While cauliflower is roasting, in a blender combine almond milk, cashew butter, nutritional yeast, and garlic. Purée until smooth and creamy. Season to taste with salt. Transfer to a small saucepan and simmer to warm.
- Remove roasted cauliflower and leeks from oven and combine with “cheese” sauce in an 8-inch square baking dish. Return to oven. Bake for 5 to 7 minutes longer, until mixture is hot.
- To serve, divide between individual serving dishes, sprinkle with chives, and serve hot.