Steam cauliflower and pumpkin until very tender. Reserve cooking liquid.
Rinse soaked macadamias.
In a high speed blender or food processor, combine rinsed macadamias, cauliflower, pumpkin, 1 cup, hot cooking liquid/boiling water, coconut milk, lemon juice, nutritional yeast, turmeric, onion and garlic powder and salt. Blend until smooth. Adjust seasoning to taste.
Meanwhile, cook elbow pasta until al dente.
Stir sauce through pasta and serve hot.
Garnish with chopped chives and a light sprinkle of nutritional yeast (optional).
For fussy kids, you can also use mashed potato in place of cauliflower.
You can also add a pinch of cayenne pepper or paprika.