Butternut Squash & Apple Soup

4 teaspoons garam masala
1 tablespoon ground coriander
2 teaspoons sweet curry powder
2 medium butternut squash, peeled, seeded, and cut into large chunks
3 sweet-tart apples (Gala, Pink Lady, Granny Smith) peeled and cut into large chunks
4 large carrots, peeled and cut into large chunks
5 tablespoons olive oil, divided
Salt and pepper
2 large onions, cut into medium dice
6 large garlic cloves, minced
1 teaspoon hot red pepper flakes
2 quarts vegetable or chicken stock
½ cup half-and-half or coconut milk
1 to 2 teaspoons apple cider vinegar (optional)

Adjust racks to lowest and highest positions and heat oven to 450 degrees. Mix together the garam, coriander, and curry. Coat squash, apples, and carrots with 3 tablespoons olive oil and season lightly with salt, pepper, and half the spice mix; turn on 2 rimmed cookie sheets and roast vegetables until soft and starting to brown, stirring occasionally and switching pans about halfway through, 20 to 25 minutes.
Meanwhile, heat remaining oil in a large soup kettle or Dutch oven; add onions and sauté until soft, about 5 minutes. Stir in garlic, the rest of the spice mix, red pepper flakes, and a light sprinkling of salt and pepper; sauté until fragrant, about a minute. Add roasted squash, apples, and carrots, and enough stock to cover. Bring to a simmer and reduce heat to medium-low; continue to simmer until vegetables are very soft and falling apart, about 15 minutes longer.
Using an immersion blender (or a food processor or blender, working in batches), puree the soup until smooth. Stir in half-and-half and additional stock or water, if necessary, to achieve desired texture. Season to taste with salt, pepper, and other spices; simmer to blend flavors, a few minutes longer. If soup needs acid, stir in a couple teaspoons of cider vinegar.