Wash cauliflower, roughly chop it and place in a pot over the steam rack. Cut butternut squash in large cubes and add to the same pot. Steam until tender. You will need to take the butternut squash out earlier since cauliflower takes longer to steam (15-20 minutes).Once the vegetables are done, place them in a blender with milk and salt. Blend until silky smooth.Transfer to a little saucepan and heat up adding more milk if you feel that the sauce is not liquid enough.Serve over pasta