In ether a big pot on the stove or your pressure cooker, saute the onion in olive oil for a few minutes. Add salt, beans and enough water to cover the beans by a couple inches. Cook until the beans are soft (about 25 minutes in the pressure cooker or 1 hour on the stove) See our guide to cooking heirloom beans.
Preheat oven to 350 degrees.
Cut the cauliflower into florets, including the stem. Toss them in olive oil, dust with salt and roast on parchment.
Roast the cauliflower for 20-30 minutes until soft, watching closely to see that it doesn't brown. If you start to see browning tent with aluminum foil. This will keep your soup from turning brown.
Remove all but a handful of the smaller more attractive florets that you will use as a garnish. Choose the biggest and least browned cauliflower for the soup base and the smaller more browned ones for the garnish. Place the garnish florets back in the oven and turn up the heat to get them beautifully brown and caramelized around the edges.
Working in batches in your blender or food processor blend the beans including the liquid and everything in the pot with the roast cauliflower, white pepper and vinegar. Blend on high until smooth, adding additional water if it is too thick. Taste and add additional salt and pepper to taste.
Ladle the soup into bowls and top with a generous sprinkle of za'atar and sumac. Place the roasted cauliflower you set aside on top of the soup and then drizzle additional olive oil on top. Serve immediately.
Caramelized onions, toasted cumin and a cinnamon stick add layers of flavor and complexity to something we normally view as just a carb canvas for other food. You'll never make basmati rice another way.
Our southwestern riff on the 3 sisters includes the True Red Cranberry Bean.This rare heirloom had been used by Abnaki Indians centuries ago but became extinct shortly thereafter. Thankfully seed savors revived it but now it is only grown by a handful of farmers.