Heat the oven to 425F. Toss the sweet potato cubes, onion wedges and unpeeled garlic cloves with the olive oil, salt and pepper and spread them in a single layer on a sheet pan with space between the pieces. Tuck the thyme sprigs among them.

Roast 30 to 35 minutes, until the cubes have properly browned edges and a few dark caramelized corners. Use two pans rather than crowding one, since a crowded pan steams.

Squeeze the roasted garlic out of its skins once cool enough to handle and discard the thyme stems.

Warm the cumin, smoked paprika, cinnamon and cayenne in a dry pot over medium heat for 30 seconds, then pour in 3 cups of the chicken broth and bring to a simmer.

Blend the roasted vegetables, roasted garlic and hot broth in two batches for 30 to 40 seconds each, no longer, or the soup turns gluey. Fill the blender no more than two thirds, remove the center cap and cover the opening with a folded towel.

Return the puree to the pot over low heat and add more broth a little at a time until the soup coats the back of a spoon and settles flat again in a second or two.

Off the heat, stir in the heavy cream, then the cider vinegar, and season with salt to taste.

Serve with a swirl of cream across each bowl, toasted pepitas, chives and cracked black pepper.