Cut the squash, the peppers, celery, carrots, one of the garlic cloves and sprinkle with oil and butter. Place into a roasting pan with some water and a lid or aluminum foil.
In a large pot, pour in 4 cups of water with the bouillon cube. Add the potatoes, cut into quarters. Add the onions and poultry seasoning, and add the other clove, diced. Bring to a simmer.
After an hour or until the squash is soft in the centre, remove from the oven and add the vegetables except the squash, it needs to cool down.
At this point, add the all spice, nutmeg, cinnamon and ginger to the cooking broth. And simmer gently.
Once the squash is cool enough, scrap the flesh out and add to the soup. Add the milk and sugar. Stir to combine. Add the salt and pepper as well, and the cayenne pepper. Simmer again.
Get a blender or food processor out and carefully blend the hot soup. Keep it separate from the stock in the pot. Blend until just smooth, some chunks are perfectly fine. Add salt and pepper to taste. Reheat and serve.