Place broth and whole sweet potatoes into pot, or Instant Pot insert pot. For regular stove top, gently boil until fork-tender through to the center. For IP, place lid on, close steam vent, choose Manual and adjust time to 10 minutes. When timer goes off allow 20 minutes for it to cool naturally, then place towel over steam vent, press Cancel and open steam vent.
Remove pot for heat and allow sweet potatoes and broth to cool for 15-20 minutes. If using IP, unplug machine and remove insert pot to allow cooling.
After elapsed time, place the following into high-powered blender: sweet potatoes (unpeeled) and broth, 1/2 cup chestnuts, fat of choice, fresh sage and sea salt. Blend for about 30 seconds until smooth.
Transfer puree to medium size saucepan and reheat. Stir in final 1 cup chestnuts. Serve, garnished with about 2 Tablespoons bacon per bowl.
Additional topping suggestions include the following: sauerkraut for a sweet and sour flavor, coconut cream or raw cream, sauteed caramelized onions, a drizzle of toasted sesame oil or extra-virgin olive oil, fresh sage, fried sage.