Preheat oven to 180C.
Cut the broccoli into small florets and dice the broccoli stem. Trim, wash and slice the leek.
Melt margarine in dutch oven over medium heat. Add leek and stir for 2 minutes until fragrant. Add broccoli stalks and garlic and continue to cook for a further 2 minutes.
Add cashews and spinach. Continue to stir until spinach has wilted. Add onion powder, flour, paprika, nutritional yeast, salt, pepper and stir until well coated.
Gradually add vegetable stock and soy milk, stirring constantly. Add miso paste and apple cider vinegar. Simmer for 5-10 minutes until mixture has thickened.
Meanwhile, in a seperate pot, boil the broccoli florets until just cooked - they should still have a bit of crunch.
When the sauce has thickened, remove from the heat and transfer to a high speed blender. Blitz until smooth.
Return the sauce to the dutch oven, add drained pasta and broccoli florets. Mix well and smooth the mixture down with a spoon.
Combine topping ingredients in a medium mixing bowl and mix well.
Add the topping to the mac n cheese, then bake for 30 minutes until golden. Serve immediately.