Press the sauté button on an electric pressure cooker. Add the turkey and brown the meat, using a wooden spoon to break it into small pieces as it cooks, 4 to 5 minutes. Drain the meat and transfer it to a small bowl.
In the pressure cooker (still on sauté), melt the butter. Add the onion, carrots, celery, and garlic. Cook, stirring, until softened, about 5 minutes. Add the flour, salt, and pepper to taste and cook, stirring, for 1 minute to cook the flour. Return the turkey to the pressure cooker and add the chicken broth, potatoes, and cauliflower and stir.
Seal and cook on high pressure for 10 minutes, until the potatoes are soft. Quick release, then open when the pressure subsides.
Transfer the cauliflower and 1 cup of the liquid to a blender and blend until smooth. Pour the puree into the soup and stir well. Add the cheddar and stir until melted. Serve topped with the scallions.
To make this in a large pot or Dutch oven, sauté over medium-high heat in steps 1 and 2. For step 3, bring to a boil, then cook, covered, over low heat until the potatoes and cauliflower are tender, 25 to 30 minutes. Transfer 1 cup of the liquid and the whole cauliflower to the blender, and blend until smooth. Stir the puree into the soup, add the cheddar, and serve topped with the scallions.
*Read the label to be sure this product is gluten-free.