Preheat the oven to 425 degrees. Line a large baking sheet with parchment paper. Slice the potatoes into wedges and lay them in a single layer by color (separating the purple ones). Break the cauliflower into small pieces with your hand, or cut with a knife. Also lay out in a single layer. Brush on the olive oil, then sprinkle everything-but-the-bagel spice on both the potatoes and cauliflower. Sprinkle the turmeric just on the cauliflower. Bake for 25 - 30 minutes until potatoes are golden brown on the edges and the cauliflower is softened. Once the veggies are done roasting, remove them from the oven. Keep the purple potatoes on the baking sheet, but transfer the yellow and red ones into a high speed blender. Also add the cauliflower, milk, broth, and salt. Using the soup functionality on your blender (or high for about 45 - 60 sec), blend until smooth. Serve soup hot with purple potatoes, sesame seeds, and green onion.
