In a roasting pan, coat the potatoes, carrots, parsnips, and celery root in just enough extra-virgin olive oil to coat, then season with salt, pepper and nutmeg. Roast the vegetables until tender and caramelized at edges, about 40 to 45 minutes.
Puree the vegetables in batches with the stock and transfer to a soup pot. Season the soup with honey and hot sauce, to taste. Cool and store for make-ahead meal.
To reheat: Reheat over medium heat.
For the cheese sandwiches: Preheat the oven. On the night you want to serve the soup, arrange a cooling rack over a baking sheet and assemble 2 cheese sandwiches using 2 bread slices and 2 slices cheese per sandwich. Cube each sandwich into 9 mini-sandwiches and separate in a baking sheet providing space between each mini-sandwich. Coat the sides and tops of each sandwich with cooking spray. Bake in the hot oven until golden and cheese melts. Float a few sandwich-croutons in each bowl of the soup bowls.
Roast 2 heads at the same time for Roasted Pepper and Eggplant Marinara, another make-ahead meal below.